3D map

Cartography is one of the most ancient and at the same time, one of the most modern sciences. The three-dimensional (3D) technologies, and the application of modern techniques give us evidences for development of cartography as a science and practice of map making. Every cartographer takes attention to users, every map should supply users with necessary information for represented objects and phenomena. Many scientists (Petrovic 2001, Bonchev 2009, Stanek et al. 2010) use this new direction for cartography to identify and evaluate different user requirements and needs.
Adami and Guerra (2006) outlined the integration of the acquisition, management and representation techniques for geo-referencing data processing. They wrote about “more representative” and “world widespread” digital cartography. This means that when reality is described and visualized, social, economic and cultural data should also be included. Second more users can be identified from different cartographic product user groups. We could conclude that 3D maps are the most suitable products for this purpose (Adami and Guerra 2006). There are many examples of 3D maps or models of reality made by different technologies with very high usage. Some examples are given below:
- The Brisbane city 3D model, built by produced using artificial intelligence (AI) photogrammetry method from the different sources: OpenStreetMap (OSM) data, Open Source Digital elevation model (DEM) LiDAR data, Free satellite imagery, shows city development and planning processes (Snecket, 2019);
- Häberling et al (2008) explain that 3D maps can be presented on a large variety of display media. They demonstrate this by presenting a 3D map from an interactive atlas of Switzerland consisting of topographic content, draped semi-transparent satellite imagery and hypsographic coloring;
- Ski trail maps in North America are represented mainly by painting, illustrated maps, annotated photos and only 3% by computer rendering (Tait 2008). In the same research, it is mentioned that for all ski areas, 17.8% of websites had an interactive map;
- Yonov and Bandrova (2018) represent a 3D map of sport area and symbols and consider cartographic aspects in map making process.
- There are many other examples which show the 3D maps applications which number rises very fast – Earth View-Map 3D of Microsoft, Earth 3D Map, 3D Imagery in Google Earth, Satellite Maps 3D Scene of NOAA, Google Cities in 3D Program, and others.
One more example is one application of 3D modelling of mountain territory which is not developed enough. Despite the development of the digital technologies, many traditional paper-based cartographic tools are still in use for different purposes (Stanek et al. 2010).

How cartography can be developed to suit producing 3D map or when 3D model can be called a 3D map? The major advantage of 3D cartographic modelling is that once a three-dimensional model is created it can be used for different purposes. It can be seen as a database and source material for the production of various types and functional applications, targeted to different areas of interest.

Content of 3D map
The concrete content of the 3D map is designed after the definition of objects and phenomena that will be included. It could be subdivided into three themes:
- main content - large topographic or landscape objects such as relief bodies, roads, buildings etc. Most designed 3D maps, presented by different companies in the world, represent it;
- secondary content, carrying the basic information. For example, in 3D urban maps – “small” objects, represented by symbols – traffic signs, facilities, transport elements, information signs, trees, etc;
- additional content, providing the quality and quantity information about objects, often created as a textual database, regarding each of designed objects or the map as a whole.
Because the objects from main content usually are represented in real size and often they are photo-textured we can consider them as a 3D model of real environment/ city. The symbol system is represented in secondary content and more qualitative and quantitative information about represented objects and phenomena could be found in additional content. We can consider that a 3D map contains all three types of content: main, secondary and additional. In addition, for every cartographic product, as a 3D map is, accuracy, scale and generalization are important elements.

Scale in 3D maps and projections
The term “Scale” in 3D maps has more complicated understanding than in 2D maps. The range of scale that can be generated in a 3D map is a huge. At the highest magnification of a section of the map or symbol, details in real size can be seen (Scale 1:1). However, this can be useful in extremely small cases, e.g. for more accurate positioning. The computer screen will limit us in the size of the map we will handle. In this case, not only the dimensions of the objects are scaled, but also the distances from their reference or reference points to the center of the scaling. Otherwise, each individual object or character can be scaled against its own reference point. Then the distances between the reference or reference points of the objects and the symbols remain unchanged. A third case of volume scaling with the same properties relative to the origin of a coordinate system can be used.
In a research with map users about scale understanding in 3D maps, most of the respondents (46.7%) answered that 3D maps can be divided into three categories: large, medium and small-scale, depending on the area of visualized territory; 40% of respondents marked “Yes, scale depends on zooming” and also 40% marked “Yes, scale depends on Levels of Detail”. Only two people (13.3%) have answered “Yes, Scale depends on data source” (Bandrova and Bonchev, 2013). This shows that the map users trying to connect the scales in 3D maps to concept of the 2D maps’ scale, even some of them make some differentiations.
Because the 3D map visualization is made very often in perspective projection the visualization of scale could be only for orientation (Figure 1). To be used for metric needs, we can visualize a map in parallel projection (Figure 2). Of course the best way for scale figure positioning is dynamically change in the model in order to reflect the correct scale at the point of placement. Anyway it will be visualized for users’ orientation and measurements could be done by electronically.

Figure 1: Scale representation in perspective projection of 3D map*.

Figure 2: Scale representation in parallel projection of 3D map*

*The figures are made by diploma student Nikola Yonov and with a leadeship of Temenoujka Bandrova

The difference between a 3D model and a 3D map
The terms 3D map and 3D model (urban, mountain, etc.) can be considered similar, and the second concept can be defined as an abbreviated version of the first concept. It is true that every map is a model of the real environment, of certain real objects or phenomena, but not every model is a map. The question of which 3D model exactly is a map needs to be clearly clarified. The answer to this question lies in the history of modern cartography. 3D topographic mapping marks the beginning of this new section of cartography, used mainly for military purposes. Tempfli defines it as extracting information about topographic objects from images or their digital representation in the form of geometric, semantic and radiometric properties of these objects. Geometry gives shape, size, location and topology. Location is defined in a three-dimensional Cartesian coordinate system (e.g. topocentric). Topology is described by the spatial relationships between objects and their components (Tempfli 1998). Goodchild writes about the paradox of modern cartography, giving an example of the flat 2D view of the world and the distortions that must be supplemented by perspective views shown in the latest versions of the Atlas Encarta from Microsoft. He notes that the "average" user will work with the digital globe more conveniently and easily than with the digital Mercator projection, "and children understand this globe more easily than its earlier projection version" (Godchild 1999). In Berlyant's definitions we find the modern view of cartography and the map, and when they are globally established, it will not make sense to consider the 3D map as a kind of new type of cartographic model, as well as its separate definition. He wrote "cartography is considered as a science of systematic information - cartographic modeling and exploration of geosystems, and the map - as a figurative-symbolic geo-information model of reality" (Berlyant 1996). Here it can be summarized that the 3D map should be considered as a cartographic model of the reality. The concept of 3D model only gives direction in the large classification order of cartographic works regarding their dimensionality, but does not determine the essence of the map. The 3D model of real environment will become a 3D map when all the elements of 3D mapping are applied to it.
3D maps represent urban or rural environments, objects, phenomena and territories well. In addition to materials used such as photogrammetric or remote sensing data a variety of often-input data can also be used for this purpose. Such information is automatically imported into most modeling systems, which facilitates the repeated usage of such data in 3D maps.
The input of a symbol system, accuracy, generalization, and other cartographic elements will help the compilers as well as users of 3D maps. Their existence will standardize 3D maps. The next step is to make research about the qualitative and quantitative features of the maps, using 3D GIS, extract data for them and solve of different kind of managers and engineers’ tasks. It will also be necessary to analyze and test the 3D maps with different groups of users.
Every 3D map consists 3D geometry, topographic information and photorealistic texturing, 3D symbols, which contain quantitative and qualitative information about the objects, north direction and coordinate datum, scale, level of details, generalization, accuracy, toponyms, legend and title. All these cartographic elements will make possible 3D model of real environment to be considered as a 3D map. Virtual camera, shades, lights, animation are new cartographic elements which should be add to the 3D map and should be discovered for future needs.