Cartography is "the science or art of making maps" (Merriam-Webster 2020). The broad objectives of cartography are:
- Creating maps that are useful
- Creating maps that are beautiful
The balance between those two objectives is dependent upon the intentions of the cartographer. There are maps that are created entirely as works of art with no clear utility, and there are maps that are designed to be entirely functional with little aesthetic consideration. However, most cartographers strive to achieve both objectives within the needs and constraints of a particular project.
The determination of whether a map is "good" or not is subjective and evaluated within the norms of the community where the map is created and used. However, there are cartographic techniques and conventions that have been developed by cartographers over hundreds of years of map making that are commonly accepted in the cartographic community. This tutorial will cover some high-level cartographic design concepts.
This tutorial draws heavily on chapter 12 from Slocum et al's (2009) Thematic Cartography and Geovisualization, and you should consult that text if you want more detail on the concepts introduced here.
The layout of a map refers to how the map content is presented on a printed page or electronic display. The figure below shows some layout elements common to a variety of map designs.
Maps for figures in documents such as reports or articles have less space to present information, so cartographers either omit elements not essential to effective communication, or present that information at different points in the document, such as captions, the text of the article, or the bibliography.
This example with minimal map elements is from an article by in the Annals of the American Association of Geographers. While the map is in color, the thematic symbols vary by lightness, which will make it legible in the grayscale (black and white) printed version.
This example with a fuller set of map elements is also from the the Annals of the American Association of Geographers. Note that the cartographers have chosen to create this graphic in grayscale to avoid any grayscale printing compatibility issues.
Web maps often retain many of the map elements of traditional print cartography, but the interactive nature of web maps and the varying display sizes (smartphones to large-format monitors) creates opportunities and limitations.
This is an example of a web "dashboard" containing a map that was a popular type of website during the COVID-19 pandemic.
A thematic map "is used to display the spatial pattern of a theme or attribute" (Slocum et al. 2009, 1). For example, this is a city planning map of different land use types in Spokane, WA from their 2017 comprehensive plan.
Thematic maps exist in contrast to general-reference maps (often shortened to reference maps) that are focused on areas rather than themes, and provide general information rather than information about a specific characteristic or type of feature.
On a thematic map, graphical characteristics of thematic symbols that can be varied based on the variables in the data are called visual variables. Although area maps are used below for examples, these visual variables exist in point, line, and raster visualizations. They can also be combined, such as symbols that vary both in color and shape.
For quantitative maps, Slocum et al. (2009, 82) suggests that there are six different visual variables.
The four visual variables for qualitative data are similar, although some (like spacing, lightness, and saturation) are omitted because they do not offer adequate contrast between different categories.
Fundamental Design Principles
Intellectual and Visual Hierarchy
Monmonier (1993) asserts that there is a intellectual hierarchy or scale of concepts that governs what should be considered most and least important on a map (Slocum et al. 2009, 214).
The size, content, and arrangement of layout and thematic elements can be adjusted to increase or decrease visual weight.
The choice of which map elements get greater or lesser visual weight communicates a visual hierarchy about what is most and least important on a map.
One definition of good basic cartographic design is that the visual hierarchy in the design reflects the intellectual hierarchy. Monmonier's hierarchy (from most to least important) is:
- Thematic symbols, and labels directly related to the theme
- The title, subtitle, and legend
- Base map information (boundaries, roads, place-names, etc.)
- Scale bar and north arrow
- Data source information
- Frame and neat lines
In cartographic design, feature contrast refers to "visual differences between map features that allow us to distinguish one feature from another" (Slocum et al. 2009, 215). Clear feature contrast facilitates clear communication of quantitative and qualitative information, and adds aesthetic appeal by providing visual variety.
The concept of figure-ground relates to methods for "accentuating certain chosen objects over others by making the chosen objects appear closer to the map user" (Slocum et al. 2009, 217). Whereas the concept of feature contrast given above deals with how thematic symbols should relate to each other, figure-ground relationship deals with how the thematic symbols relate to other map elements.
When the outlines of the thematic symbols do not clearly indicate the area being depicted, a reference base map is commonly placed under the symbols to give geographic context and help map viewers know what location on the surface of the planet is being depicted in the map.
When a base map is used, a clear figure-ground relationship is present when the thematic symbols are styled to be clearly distinguishable from the base map, and the base map is styled so that its symbols do not clash with the thematic symbols.
For well-known geographic areas (such as the world, or US states as a whole), no base map may be necessary and may add clutter. However, when mapping a local area that may be unfamiliar to the map users, a base map can provide useful geographic context to understand the relationship between the phenomena being depicted, and the real-world locations of that phenomena on the surface of the planet.
Balance is "the organization of map elements and empty space that results in visual harmony and equilibrium" (Slocum et al. 2009, 218).
The concepts of harmony and equilibrium are subjective, and achieving those qualities in design often require some level of experimentation with a particular map design, including symmetry (or balanced asymmetry) and maximal utilization of space.
Cartographic Design Procedure
Creation of maps that utilize these design principles can be facilitated by a systematic approach to each project that forces consideration of those general concepts in the context of the specific requirements of each particular project.
The classical waterfall technique is a requirements-driven approach that involves clear definitions of the specification for the project up front, with design following only after those specifications are codified. This approach is most effective where the data and the ultimate objectives are clear from the beginning, and the cartographic layout will be complex, such as for an urban planner preparing a map of proposed zoning changes for a public meeting. This approach dates from a time when data was scarce, and cartography required difficult, time-consuming manual drafting work to create compelling visualizations.
However, there are commonly situations (notably in research) where a complete understanding of the data or the ultimate objectives are not clear from the beginning of the process. Exploratory data analysis is an iterative, data-driven approach that integrates cartography with the research process. This approach is possible because of the availability of comparatively fast and inexpensive GIS technology, as well as increased availability of massive amounts of geospatial data.
In practice, elements of both approaches are often used, and thinking through your projects before expending the often extensive amount of time needed to create a complex cartographic design is usually a preferred approach that ultimately can save time and effort.