Method for Cartographic Symbols Creation in Connection with Map Series Digitization

ISPRS Int. J. Geo-Inf. 2022, 11, 105. https://doi.org/10.3390/ijgi11020105 www.mdpi.com/journal/ijgi Article Method for Cartographic Symbols Creation in Connection with Map Series Digitization Dalibor Bartoněk * and Pavla Andělová Institute of Geodesy, Faculty of Civil Engineering, Brno University of Technology, Veveří 95, 602 00 Brno, Czech Republic; andelova.[email protected]br.cz * Correspondence: [email protected]br.cz Abstract: The article addresses the issue of the unification of cartographic symbols in terms of graphics (visual) and interpretation in an international context. The motivation is the ongoing digitization of processes in the conditions of Industry 4.0, especially Construction 4.0, where geodesy and cartography have their irreplaceable share. The aim was both to design uniform cartographic symbols for the description of geographical objects on the map and to design a general method for the description of unified cartographic symbols so that it is independent of specific applications. The authors compared the symbols used in the map works of the Czech Republic and neighboring countries that are members of the EU and proposed a formal description of the graphics properties of the symbols, which is based on a general mathematical model. The description takes the form of a text string, and a Python algorithm was built to render the symbol and implemented in the QGIS environment. The article also presents a comparison of some cartographic symbols used in the Czech Republic and in selected EU countries and a proposal for their unification. The motivation is the effort to unify the cartographic language within the EU. The problem is in accordance with the INSPIRE directive (seamless map of Europe) at the international level and with the Digital Czechia 2018+ strategy at the national level. Keywords: cartographic symbol; maps digitization; automated drawing of cartographic symbols; design of cartographic symbols; formal description of cartographic symbols 1. Introduction The present time is characteristic of extensive digitization in almost all fields of human activities. In the Czech Republic (CR) a strategy for coordinated and comprehensive digitization of the Czech Republic 2018+, in short, “Digital Czechia”, was accepted. One of the sub-targets of this strategy is an item called GeoInfoStrategy. It is about the effective use of spatial information in the state administration and in the public interest. This category also includes the digitization of national map series and relevant cartographic products. World map products differ in their content, various coordinates, vertical systems, projections, and cartographic languages used. One of the many projects that have been in this area is the research and development of software for state map series generalization addressed in [1]. Within this project was the modification of the symbol key also solved, the aim of which were: • Enrichment of the brand key with new elements or attributes from other databases, • Unification of the brand key across all scales, • Bringing the brand key closer to the form of other brand keys for better usability of the transmitted data, • Brand key to an automated mapping process adapting and avoiding the need for manual adjustments (resizing or color). Part of this project was the study of cartographic symbols, the possibility of unifying Citation: Bartoněk, D.; Andělová, P. Method for Cartographic Symbols Creation in Connection with Map Series Digitization. ISPRS Int. J. Geo-Inf. 2022, 11, 105. https://doi.org/ 10.3390/ijgi11020105 Academic Editor: Wolfgang Kainz Received: 14 November 2021 Accepted: 31 January 2022 Published: 2 February 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/license s/by/4.0/). ISPRS Int. J. Geo-Inf. 2022, 11, 105 2 of 23 the set of symbols in an international context, and their use in digitized map products. Currently, the standardization of symbol sets for printed maps is not still satisfactorily resolved at national levels. In the case of map production using information technologies, the standardization is only reflected in metadata structure and used system formats. Currently used cartographic symbol sets are stored in different software (ArcGIS, MicroStation, etc.) in libraries that are not fully compatible among particular application software [2–5]. Methods for users to create new symbols or to modify existing symbols are not unified across the software. This situation limits the process of map product digitization across all platforms and their common use on a national and international scale. In connection with the massive advent of digitization, the solution to these problems is very urgent. A considerable number of projects, works, and studies have been devoted to the issue of the digitization of maps. Projects at the European level include the European Interoperability Framework (EIF) [6], which aims: • To promote and support the delivery of European public services by fostering cross-border and cross-sectoral interoperability; • To guide public administrations in their work to provide European public services to businesses and citizens; • To complement and tie together the various National Interoperability Frameworks (NIFs) at the European level. Interoperability of data, services, and technologies is enabled by international technical norms and standards (ISO, OGC, etc.). The initiators of these activities are the INSPIRE directive, Euro-Geographics, etc. In the Czech Republic (CR), the issue of unification and creation of cartographic symbols is addressed in several follow-up projects with the support of the Technology Agency of the Czech Republic, for example [1]. The aim of this article is to propose a suitable methodology for the creation, formal description, unification, and automatic drawing of cartographic symbols in the digital map series. The paper is organized as follows. In Section 2, we mention some related work concerning cartographic symbols. In Section 3, we describe problems regarding cartographic symbol creation and propose the method of a possible solution. Section 4 demonstrates the experiments. Section 5 contains a discussion of the given topic. Section 6 addresses the conclusions. 2. Related Works The topics selected in this section are directly related to the goal defined in the previous chapter. The methods of formal description of cartographic symbols are described in [7–9]. The aim was to find out existing ways (methods) of finding common descriptions of cartographic symbols that are platform-independent (desktop, web application, etc.). A proposal for a new cartographic language paradigm that would suit the map series of various states and thus make international collaboration in this field possible is presented in [7]. Authors do not propose the creation of individual cartographic symbols, but a cartographic language as a whole. They solve language style issues in various state map series, specific national conventions, and problems with cartographic symbol standardization. Authors propose a completely new cartographic language alphabet based on GIS templates that are more usable than conventional pixels or symbols. Templates of variable GIS icons support additional graphic elements including length/width/shape/angle/orientation. Numerals, alphabetical characters, and iconographic symbols can be used as variables. The benefit is the possibility of visualization of multidimensional data relationships. Problems with the proportional size of cartographic symbols are solved in the work [8] by programming language R. This method is general and allows for both mathematical and perceptual scaling in the process of displaying the ISPRS Int. J. Geo-Inf. 2022, 11, 105 3 of 23 symbols. There is no solution for the complex description of cartographic symbols graphics including attributes (color, thickness, line type, etc. The article [9] deals with linear cartographic language creation in the programming language C++. The creation of linear cartographic language creation in the programming language C++ is a topic in [9]. The algorithm concept primarily presents symbol visualization on digital maps with respect to cartographic rules and valid standards. The formal symbol description is very similar (including rendering) at the expense of complexity and generality. The design of cartographic symbols including special symbols (user symbols) with regard to currently used symbols in EU states and their compatibility with applications for map production (GIS SW) is shown in [3,5,10–15]. Methods of cartographic symbol creation in a GIS environment (ArcGIS) and on the website (Web Map Services) are discussed in paper [3]. Cartographic symbols were created in the application CorelDraw and imported into the ArcGIS library via Font editor. National and international standards were respected during symbol creation. The advantage of this concept is the possibility of using symbols in both GIS environments and web applications. The disadvantage is a partial dependence on specific platforms (CorelDraw, ArcGIS). The use of random variable configurations and boundaries for the creation of cartographic symbols is a topic in [11]. These generating algorithms are limited by shape elements, cartographic standards, and many other conditions. The method is based on fractal geometry, namely the iterated function system (IFS). This method was implemented into a digital mapping system for practical use. The essence of symbol generation is inspiring, but the limited use of symbols with randomly planar patterns is a disadvantage. A cognitive geometry model for cartographic symbols realization is proposed in [12]. Its advantage is usability not only on two-dimensional maps but also on digital maps, maps animation, and cartography for blind users. Another advantage of this model is precise data source representation and an intuitive understanding of the phenomena that symbols represent on the map. However, the article does not indicate the methodology of symbol creation, their inclusion in applications, and binding to valid standards. The paper [5] describes cartographic symbol creation for geological maps. Symbols are defined with the aid of XML language and stored in the library. However, the library is dependent on the application and was specially developed for GIS Manifold®. Symbol definitions are simple and sufficiently common, so after some modifications, they can be used in other GIS programs. Special standardized cartographic symbols set for planetary mapping based on the American standards for geological exploration are presented in [13]. Symbol sets are implemented into the GIS system, namely ArcGIS. This is a contribution to space research presentation and subsequent interplanetary space mapping. A new methodology for creating two-dimensional cartographic symbols and diagrams for application in thematic maps is described in [14]. The proposed method extends two construction theories of Bertin [10] and Wilkinson [15]. The benefit is improved visualization of statistical data on thematic maps. Problems of map product digitization are the topic of [16–23]. The aim was to discover problems that result from a transfer of classic analog to digital form maps. A method for creating map legends in a dynamic environment is introduced in [16]. These legends were developed for static media with respect to optimal map visualization. The main criteria for the design of legends are element selection, symbols layout and their position, representation dynamics, and other factors. Cartographic symbols appear here only as legend components without further context. A multi-level hierarchic spatial model is designed in work [17]. Objects with increasing detail are stored in levels and can be used in the composition of maps at some scale. The method can also be applied to a specific display of cartographic symbols on a definite map at some scale. The problem of symbol creation is not solved in this paper. Geologic maps are characterized by very extensive and complicated legends. A new flexible legend that offers a lot of diverse geo- ISPRS Int. J. Geo-Inf. 2022, 11, 105 4 of 23 morphological information and possibilities of many information combinations is proposed by the authors of [18]. The result is a scientific data-rich map that is more informative than most maps used until now but is based on a simple legend. The developed system uses GIS applications as a base. Information based on geomorphological map symbols can be stored digitally and can be used as an efficient database with thematic levels and attribute tables. The advantage of this method is the simplification of the legend, but this does not address the concept of cartographic symbols creation in the legend. Graphics, numbers, and optimal distribution of buttons with inserted functions in applications for mobile mapping and maps presented in a web environment are described in [19]. The problem of symbols creation and standardization is not solved in this work. With the integration of cartographic symbols that come from different sources into united map output deals [20]. The research results were primarily for mobile devices for LBS (Location Based Services) and intended to accept spatial data from various providers. The conception is based on ontology and has general utilization. The article does not resolve the symbol creation issue, only their selection in a common map. Several selection rules ensure the avoidance of symbol duplication. A hierarchical classification system for thematic cartography is proposed in paper [21]. The system was applied to atlases in the Czech Republic and the Slovak Republic from 1935 until now. The contribution of the work is a method for the time series analysis of cartographic products and their subsequent classification in terms of topics and logic. The article [22] proposes the method for the automatic selection of point height positions that represent natural features as peaks, saddles, or depressions. The algorithm and data structure are designed for a continuous scale. The contribution is a result comparable with manually created reference compilations. This research does not solve the cartographic symbol creation issue but introduces an interesting method for other use of these symbols. The algorithm for automatic contour line generation according to cartographic lines is proposed in the article [23]. This algorithm deals with supplementary contours selection and automated methods for their placement on topographic maps. Results of this method are similar to manually placed supplementary contours. The method is suitable for digital terrain model creation and is a rewarding contribution to map digitization. Methods for automated visualization of cartographic symbols are the topic of several works [4,24–28]. This part deals with symbol selection from a suitable database, their positioning and plotting in a map face using automated tools. A method for the visualization of proportional cartographic symbols on a map is presented in [24]. The algorithm is based on a decomposition of an original symbol to components and their hierarchical synthesis and contains tools for display optimization. With respect to the concept, this approach is similar to ours. The study [4] presents possibilities of cartographic symbols’ dynamic visualization on digital static maps. The proposed methods were based on a series of visual tests, parameters of dynamic symbols visualization (intensity and frequency of blink, size, etc.), and their optimization in relation to the current scale was evaluated. The publication [25] presents a proposal of a method for the improvement of visualization of cartographic symbols stored in the GIS applications library. The symbols’ proposal is based on the aliasing repression and solves mutual relations between particular symbols. The proposed method is also inspirational for the topic solved in this article. An effective method for linear cartographic symbols depiction in 3D is described in the paper [26]. It is about an acceleration algorithm for GPU (Graphics Processing Unit). Due to this, symbol depiction can be in almost real-time executed. The authors of [27] deal with perceptional aspects of graphic variables (namely shape and size), the problem of chosen and map background during cartographic visualization. The benefit of this study is understanding map users’ reactions to various cartographic symbols in different cultural conditions. These experiments were accomplished in the Czech Republic and China. The proposal and implementation of variable POI (Points Of Interest) symbol models is the topic of [28]. The benefit is improved symbol visualization on digital maps in a web environment based on principles of cognitive psychology. ISPRS Int. J. Geo-Inf. 2022, 11, 105 5 of 23 It is clear from relevant literature that problems of creation, formal description and visualization on digital map products are solved from many perspectives and in various contexts. All the presented methods are inspiring, and include original ideas, but none of them solve this problem comprehensively. Cartographic symbols creation is application-dependent in many cases. The methods proposed for the description of cartographic symbols are, in many cases, based on Cascading Style Sheets for Maps—CartoCSS [29] or OGC (Open GeoSpatial Consortium) Symbology Encoding [30]. The advantage of these tools is their versatility and flexibility, the disadvantage is the relative complexity of the description and the need to know the syntax of these languages, which requires good knowledge of information technology. The method proposed in this article tries to remove the previously mentioned problems. 3. Materials and Methods The aim, described in Section 1 (to propose a suitable methodology for the creation, formal description, unification, and automatic drawing of cartographic symbols in the digital map series) was delivered in two parts: 1. Analysis of cartographic symbols in map series in CR and related EU states in order to design a uniform symbol set. 2. Proposal of a suitable method for the description of cartographic symbols. 3.1. Analysis of Cartographic Symbols in Map Series in CR and Selected EU States in Order to Design a Uniform Symbol Set This topic was in [31] and [32], basic results are presented in Section 4.1. Project [1] was solved under the cooperation of the Czech Office for Surveying, Mapping and Cadaster and Institute of Geodesy, Faculty of Civil Engineering, Brno University of Technology (both Czech Republic). Given the significant historical development of the features used in the national map series of the EU, it would not be right to reject these features and design completely new ones. On the contrary, it is more advantageous to support this development and thus use these symbols for the new uniform symbol set. The biggest advantages lie in the experienced features of both map users and makers, but also in the fact that they are tested for use in practice. As the features in each country have evolved, it can be assumed and even desirable that the newly created single set will undergo evolution with the necessary changes and adjustments. However, it is not possible to take a set of symbols from one country and declare it the best that should be used throughout the European Union. A single symbol set should be created by comparing and evaluating matching symbols. Considerations on a uniform symbol set should thus begin with the selection of countries whose symbol sets will form the so-called basic symbol selection group. The used selective method with predetermined conditions thus determines the symbol sets that will enter the analytical part of the work. Reducing the number of countries for comparison will make the comparison analysis more efficient. One of the main selection criteria should be the number of people who are already related to the field. Because the more inhabitants the state has, the more users are already used to its state symbol set. If the symbol sets of the most populous countries are combined, fewer users will have to learn new symbols. This condition mainly concerns users, but we must not forget the map creator either. It can be assumed that the larger the area, the more people must participate in the creation of the state map. These two considerations combine the criterion of population and area of states to select a basic group for comparing features. At the same time, the selected countries should represent the majority of the European Union in both area and population. The number of states was reduced during the project processing on the basis of cooperation with the Embassy and it needs further reduction. In the end, the work is pri- ISPRS Int. J. Geo-Inf. 2022, 11, 105 6 of 23 marily aimed at the countries of Central Europe, that is, the Czech Republic and neighboring countries. Next, comparisons and detailed analysis of the graphical variables of the corresponding features helped to reveal the trends of contemporary national cartographic languages and their similarity or, conversely, diversity. The manual visual comparison of graphic variables was performed by the research team and subsequently evaluated by the authors in a quantitative and qualitative comparison. A similar comparison was made due to the history of the symbols used on the maps of Czech state map works in order to reveal the trends in the development of cartographic language in CR. This analysis was also performed by the visual comparison of graphical variables and resulted in quantitative and qualitative outputs. 3.1.1. The Process of Accepting New Symbols The design of the new features then took place on the basis of a discussion among experts from the cartographic section of the Embassy, their experience with problematic situations in cartographic interpretation and, last but not least, with the inclusion of comments from users of state map productions. These proposals had to go through several trial publications with departmental and interdepartmental comments. All cartographic activities are subject to the Surveying Act, which, after approval by the Parliament of the Czech Republic on 30 September 1994, entered into force on January 1st 1995. Only then were they admitted to the press for public distribution. All symbols were drawn in ArcGIS and used for the automatic creation of state map series. The symbols are at the same time supplemented with detailed specifications and published in a comprehensive symbol key. 3.1.2. Factors Influencing the Comparison of Symbols The biggest obstacle for comparing symbols is the translation of their meanings because one word in a foreign language can have several Czech equivalents and vice versa. The differences between the names of the symbols are difficult to distinguish, especially when it comes to specialized objects, such as electrical or mining elements. The use of multilingual regulations and a terminological dictionary partially addresses this issue [33]. Another significant complication is the absence of dimensions. This makes it impossible to compare the symbols in detail and draw other conclusions, such as the importance of the phenomenon, etc. The comparison is thus limited to the appearance of the symbols. The biggest problem is the different ways and details of the division of elements and their hierarchical division. 3.2. Method for Description of Cartographic Symbols Afterward, we can formulate basic requirements for the method for cartographic symbols creation: There is a possibility to generate own symbols besides established standards, for example, for thematic maps. • Depiction for any scales (proportional change of symbol geometric proportions). • Possibility to modify symbols according to requirements. • Possibility to combine symbols. • Application independence. • Optimization of symbols location to map face in case of possible symbols overlap. Proposed solution concept. The authors chose the following working procedure for automated cartographic symbols generation: • Creation of a mathematical model of cartographic symbols based on graphic variables. • Proposal of a formal language for graphics description (syntax). ISPRS Int. J. Geo-Inf. 2022, 11, 105 7 of 23 • Choice of a scripting language to symbols depictions for variable scale maps. • Proposal of an algorithm and the realization of the process in a suitable application (e.g., ArcGIS, QGIS). The proposed method is shown in Figure 1. Figure 1. Concept of automated creation and usage of cartographic symbols. 3.2.1. Mathematical Model Authors Pravda [34] and Bertin [10] mention these basic graphic variables of a symbol: Shape—given by symbol contour line. Size—represents the quantitative value of phenomenon and this quantity is proportional to symbol size. Filling or texture—using colors or raster to express phenomenon quality, quantity can be expressed by different intensities of color or raster. Orientation—is important if symbols express some phenomenon’s position in relation to coordinate grid (or another object) or phenomenon development along some route. Color—characteristics used are hue, saturation, and brightness [35]. Hojovec [36] and Voženílek [37] extend these graphic variables by two more: Structure—internal graphic segmentation of symbol. It can express quantitative relations among components that form the whole phenomenon. The structure can have only esthetic sense. Position (georeferencing)—symbol location on the map using coordinates. Digital forms of cartography provide another means of expression, such as movement, blinking, or color change, etc. Problems of these variables are not explored in this work. On basis of the above-mentioned variables, cartographic symbol s ∈ S is given by depiction of f f: P x G x M x O → S, e.g.,: s = f(p, g, m, o) (1) where S is collection of cartographic symbols. The collection means that symbols may repeat in the set. This enables the creation of composed (also hierarchical) cartographic symbols and their repeated use, for example, basic symbol pattern placing on a linear element. P is the set of symbol fixed points in a map space with coordinates x, y, (z), ISPRS Int. J. Geo-Inf. 2022, 11, 105 8 of 23 G is a set of geometrical and descriptive elements with attributes of which a symbol is composed (symbol graphical variables); the set is influenced by standardization and valid legislation. They can be standard or created for a given purpose. They depend on a geographical object o ∈ O that is represented by the given symbol. M is map scale—it also influences symbol representation on a map. It influences the size of the symbol that is to be displayed. O is the set of geographic objects on a map, which are represented by the symbol (symbol semantics). When designing symbols, taking existing symbol forms in the CR and the EU into consideration is necessary. It is also important to select suitable representative symbols that would be appropriate in a wider context of use. This is a method of compromise between the modern approach to digitalization and the symbol forms used so far within the European and world cartographic communities. 3.2.2. Proposal of a Formal Language for Symbol Graphic Description (Syntax) The language for a cartographic symbol description was proposed on the basis of graphical variables and Equation (1)—see the previous subchapter. The basic idea was a description of graphic variables set by simple elements (primitives), from which it would be possible to create more complex elements using composition (e.g., a circle replaced by a sequence of line segments). The basic attributes of the symbols were classified within the information analysis in the previous subchapter. Symbolic equivalents that serve as commands for drawing were assigned to these attributes : 1. Global symbol parameters (valid for the whole map sheet or slice): • symbol ID, • x, y, (z), coordinates of symbol fixed point, • M—map scale-value M = 0 means that the symbol will not be drawing in a given scale. 2. Local symbol parameters: a) Commands for geometric elements drawing (drawing of points, lines, arcs, circles, or polygons. Coordinates relative in relation with symbol fixed point). • L = line x1, y1, x2, y2 • A = arc—add parameters • R = ring xs, ys, r (circle with center and radius) • P = polygon xi, yi (vertexes on polygon boundary) b) Commands for geometry design—color, type, and weight of the line (drawing attributes). • C = color <color ID> (color code, same as filling color code) • F = color <color ID for filling>—last defined entity (circle or polygon) will be filled with given color. Colors (C, F) will be from color table chosen. F = N means without filling • Y = type <type line number> • W = weight <weight line number> • T = text <font number>—other attributes (C, Y, W) will be adopted from geometry definition • H = hypertext—link to another object (file) in case of dynamic visualization (animation) or symbol with multimedia components. • Separators of commands are semicolons ‘;’ (alternative TAB or space). • Decimal points will be represented by dots ‘.’. The previously mentioned formal language of symbols description will be saved in a text file in this format: (line structure for 1 cartographic symbol): ISPRS Int. J. Geo-Inf. 2022, 11, 105 9 of 23 <ID, commands sequence, EOL (End of Line)>. Symbols are currently saved in application libraries in graphic formats (raster or vector). The disadvantage is a necessity for the symbol transformation for a given scale while putting symbols into the map sheet. The transformation works automatically in this method. For the proposed method, a special algorithm for drawing cartographic symbols was developed. The input of the algorithm were global data (symbol ID, coordinates of the reference point x0, y0, scale M) and a text file containing a formal description of cartographic symbols. The flowchart of the algorithm is in Figure 2. Figure 2. Algorithm for drawing cartographic symbols. 4. Experimental Results The verification of the proposed methodology consisted of three phases: 1. Processing of analysis of used cartographic symbols in map works of neighboring states with relation to the Czech Republic and the EU. 2. Design of new cartographic symbols. 3. Design and implementation of an algorithm for drawing the cartographic symbols based on the formal description. ISPRS Int. J. Geo-Inf. 2022, 11, 105 16 of 23 y0 = [ySJTSK] scale M = 100 (1:100) ID = <chapel> Symbol geometry description: It is assumed that x0 = 0 and y0 = 0 (relative coordinates): Line in Text File: ID; F = 255; R0,0,2; C = black; Y = solid; W = 1.5; L0,0,−6,0; L−4,2,−4−2; <EOL> Algorithm input parameters for symbols depiction: ID, x0, y0, M. The symbol representing the church in the environment QGIS is shown in Figure 4. Figure 4. The symbol representing the chapel in the QGIS environment. Another demonstration example of a linear symbol is shown in Figure 5. This symbol represents the difficulty of the route in maps of cycling paths [2]. This basic segment is repeated on the whole route. Figure 5. Example of linear symbol depiction (road) from the formal description. Symbol geometry description: It is assumed that x0 = 0 a y0 = 0 (relative coordinates), ID = <road with type of surface> Line in Text File: ID; F = violet; P0,0,−1,0,−1,−12,0,−12; F = black; P0,−4,−1,−4,−1,−4.2,0,−4.2; P0,−12,−1,−12,−1,−12.2,0−12.2;<EOL> The proposed method is able to describe also composed symbol. An example of an area symbol is shown in Figure 6, symbol geometry description is in the next text. ISPRS Int. J. Geo-Inf. 2022, 11, 105 17 of 23 Symbol geometry description: It is assumed that x0 = 0 a y0 = 0 (relative coordinates), ID = <area symbol: garden> Line in Text File: ID; F = green; P0,0,-8,0,-8,-12,0,-12; F = N; Y = solid; R−2.5,−3,1;R−5.5,−3,1;R−2.5,−9,1;R−5.5,−9,1; F = black; R0,0,0.8;R−2,0,0.8; R−4,0,0.8; R−6,0,0.8; R−8,0,0.8; R−8,−2,0.8; R−8,−4,0.8; R−8,−6,0.8; R−8,−8,0.8; R−8.−10.8; R−8,−12,0.8; R−12,−6,0.8; R−12,−4,0.8; R−12,−2,0.8; R−12,0,0.8; R−10,0,0.8; R-8,0,0.8; R−6,0,0.8; R−4,0,0.8; R−2,0,0.8; <EOL> Figure 6. Example of area symbol depiction (garden) from the formal description. A demonstration example of a special user-defined symbol is shown in Figure 7. This symbol represents a pub in purpose maps of cycling paths [2]—see Figure 8. Symbol geometry description: It is assumed that x0 = 0 a y0 = 0 (relative coordinates), ID = <area symbol: pub> Line in Text File: ID; F = blue; P-1,-1,-2,0,-12,0,-13,-1,-14,-2,-14,-12,-13,-13,-14,-12,-14,-2,-13,-1,-12,0,-2,0; F = white; A-10,-2.5,12,-6,-10,-9.5; L-10,-2.5,-10,-9.5; P-2,-2,-9,-2,-9,-9-9,-2; F = blue; P-3,-3,-8,-3,-8,-4,-3,-4; P-3,-5,-8,-5,-8,-6,-3,-6P-3,-7,-8,-7,-8,-8,-3,-8; C = white; W = 1; L-8,-10,-8,13;A-8,-13,-6.5,-12.5,-4.5,-10; <EOL> Figure 7. Example of user-defined symbol depiction (pub) from the formal description. According to the symbol ID, the program searches for the appropriate line in the text file and performs parsing of the text. Commands for drawing a symbol (line points, ISPRS Int. J. Geo-Inf. 2022, 11, 105 18 of 23 polygons) are identified using separators (special characters). Within each command, the symbology of individual elements (color, strength and line type, etc.) is processed and written to the appropriate layer. Finally, optional operations such as merging layers, converting from vector to raster format, and the like are performed. The algorithm was debugged in the Python scripting language in the QGIS environment. Figure 4 shows a church symbol in QGIS. This emblem was designed as a common symbol for map works in the Czech Republic and neighboring countries [32]. The symbol description according to the methodology in chapter 3.3 is (the separator is a semicolon): ID5; Fblack;R0,0,70; Cblack; Ysolid; W4.6; L0,0,−6,0; L−4,2,−4,−2; <EOL> The algorithm is sufficiently universal and can be used in any CAD, GIS, etc. application. The proposed method was verified when creating special maps for cycling. In this case, it was necessary to display the route map with additional information such as type of surface, difficulty of the road, type of road (1st, 2nd, or 3rd class road), etc. An example of these maps is shown in Figures 8 and 9. Maps for bike paths were also created for the web environment—the link is to [44]. Figure 8. Point and line symbols in a special map for cycling paths. ISPRS Int. J. Geo-Inf. 2022, 11, 105 19 of 23 Figure 9. Combined line symbols in a special map for cycling paths. It can be seen from the figures that the proposed description of the cartographic symbol is universal and allows the combination of all possible graphic elements within one symbol. 5. Discussion The digitization of maps is not just about converting maps from analog to digital formats. It is mainly a unification of methods and processes in the creation, updating, and presentation of cartographic works. Experience from practice confirms that digitization in the given field will be maximally effective, under the following conditions: • All work procedures will be the same if possible. • All processes will be as simple as possible. • Data flows between subsystems will be in machine-readable format. • Phenomena from legislation and standardization will be clearly implemented in the application software. • The information infrastructure, that is., HW and SW, will be the same at all levels of organizational units. In the field of cartographic works, the authors proposed to solve this problem on two levels: • Analysis of the current state of map production in selected EU countries in order to unify the procedures for the creation, interpretation, and publication of map works at the national and international level. • Unify the map key of the analyzed digital maps and design a method for the simple description of cartographic symbols. Given the current solutions, the presented methodology is beneficial in the following points: • Analyzes map works not only at the national but also at the international level. • It seeks to unify the map key in an international context. ISPRS Int. J. Geo-Inf. 2022, 11, 105 20 of 23 • Suggests a simple description of cartographic symbols, independent of application and national language. The symbol description stored in the text file can be considered the simplest data structure that any user can create and interpret even without special information technology. In addition, each application has the means to process text files. The paper contains examples of cartographic symbols and their description. These are just demonstration examples that prove that the proposed description is general enough to describe even complex features. The methods published so far, which dealt with the design of symbols, were conceived mostly from a certain point of view without a broader context. For example, the method proposed in the article [3] is usable in a web environment but is application-dependent on ArcGIS and Corel Draw. The method of symbol creation described in the publication [5] is very general (description using XML), but also application-dependent. Another disadvantage is that the description of symbols using XML is extensive (of considerable size), complex, and confusing. The approach to symbol creation using fractal geometry proposed in another article has similar properties [11]. Other works focus more on cartographic language as a whole than on the creation of individual symbols. These are, for example, publications [7] where the benefit is a new paradigm of cartographic language, which would suit the map works of various states and thus enable international cooperation in this field. The authors [45] then propose a completely new alphabet of cartographic language based on templates. The benefit of the method is the possibility of visualizing the mutual relationship of multidimensional data. One of the most important aspects of digitization is the unification of processes, procedures, and methods in a given field to the widest possible extent (region, state, …). To achieve this goal, it is necessary that all processes are simplified as much as possible and made understandable and easily accessible to all actors. These principles also apply to the digitization of cartographic symbols. Currently, there is a growing need for digital maps for various and specific purposes. An example of this is, for example, a collection of maps for cycling, orienteering, etc. The authors encountered the issue of the requirement for special cartographic symbols in projects [46] (marking of areas on the map, where the optimal GNSS method is recommended) [47] (symbols representing selected properties for stakeholders) and [48] (creation of output maps for classification surfaces above underground gas pipelines). A similar problem was solved in the creation of maps for crisis management [49]. These maps use very specific map features for a given purpose. The advantage of the proposed solution is its simplicity, so the cartographic symbol can be described by the end-user, who is not an expert in the field of information technology. The proposed procedure can be considered as an alternative to the methods published so far. It is therefore a method that is accessible to the widest possible public using digital maps for its activities. 6. Conclusions and Future Work This work is focused mainly on the possibility of converging cartographic symbol expression on state map works published in the Czech Republic and neighboring countries. The creation of a single symbol set is a very lengthy process involving several issued and tested sets, which can be gradually adapted to reflect the needs of the countries concerned. At the same time, it is necessary to use the experience from symbol sets that have already been published and used for several years. The gradual convergence of symbol sets between states depends primarily on the accessibility of individual state organizations. But given the involvement of countries in the European Union and in initiatives such as INSPIRE and EuroGeographics, interest in this development can be expected in at least some countries. Poland, Bavaria, and Spain, in particular, have already shown interest in this cooperation. ISPRS Int. J. Geo-Inf. 2022, 11, 105 21 of 23 It is relatively clear from the results of the comparison of the symbols used in the countries concerned that creating a complete universal set of symbols for all countries would be a very demanding and probably time-consuming process. These are mainly categories of borders and communications, where each state applies a different division, hierarchy, and definition of individual elements. This cannot simply be unified, as administrative divisions are usually deeply rooted in the historical development of the state itself. Unification or at least approximation in this category would require longer negotiations and the involvement of relevant state organizations. In other categories, it would be possible, in agreement with the competent authorities of the individual states, to adjust the displayed objects and the detail of their differentiation and at least partially unify them. In these areas, even within the development of symbols in individual countries, there are often changes, as follows from the analysis of the development of symbol sets used historically in the Czech Republic. The cartographic symbol key, which was created in this work in cooperation with the Czech Office for Surveying and Cadaster and Military Geographical and Hydrometeorological Office CZ, has so far been developed primarily for the needs of the Czech state map work. However, it is important that it was created precisely and with detailed additional information describing all the graphic variables of the symbols. At the beginning of 2020, trial production of ZTM5, ZTM10, and ZTM25 began, and further also ZTM50 and ZTM100. These pilot map sheets will gradually check the proposed features. Author Contributions: D.B. elaborated literature review, create mathematical model, designed the algorithm, and implemented Python script, P.A. has provided support materials, conducted an overall editorial of the whole article and a professional translation. All authors have read and agreed to the published version of the manuscript. Funding: This work is supported by the Specific Research Project FAST-J-20-6374 of Brno University of Technology. Institutional Review Board Statement: Review board of Faculty of Civil Engineering, Brno University of Technology, Czech Republic. Date of approval: 1 March 2020. Informed Consent Statement: Not applicable. Data Availability Statement: This study did not report any data. Acknowledgments: We greatly appreciate the careful reviews and thoughtful suggestions by reviewers. Conflicts of Interest: The authors declare no conflict of interest. References 1. Výzkum a Vývoj Programového Aparátu Pro Generalizaci Státního Mapového Díla. 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