Maps are among the most compelling forms of information for several reasons. Maps are artistic. Maps are scientific. Maps preserve history. Maps clarify. Maps reveal the invisible. Maps inform the future. Regardless of the reason, maps capture people’s imaginations around the world. As one of the most trusted forms of information, mapmakers, and geographic information system (GIS) practitioners hold considerable power and influence. Therefore, understanding and appreciating maps and how maps convey information are essential aspects of GIS. The appreciation of maps begins with exploring various map types.

There are just as many definitions of maps as people who use and make them like GIS. We can define a map simply as a representation of the world. Such maps can be stored in our brains (i.e., mental maps), printed on paper, or online. Notwithstanding the actual medium of the map (e.g., our fleeting thoughts, paper, or digital display), maps represent and describe various aspects of the world. For clarity, the three types of maps are the reference map, the thematic map, and the dynamic map.

Reference Maps

The primary purpose of a reference map is to deliver location information to the map user. Therefore, a reference map’s geographic features and map elements tend to be treated and represented equally. In other words, no single aspect of a reference map takes precedence over any other aspect. Moreover, reference maps represent geographic reality accurately. Examples of standard reference maps include topographic maps created by the United States Geological Survey (USGS) and image maps obtained from satellites or aircraft available through online mapping services.

The accuracy of a given reference map is indeed critical to many users. For instance, local governments need accurate reference maps for land use, zoning, and tax purposes. National governments need accurate reference maps for political, infrastructure, and military purposes. People who depend on navigation devices like global positioning systems (GPS) units also need accurate, and up-to-date reference maps to arrive at their desired destinations.

Thematic Maps

Contrasting the reference map are thematic maps. As the name suggests, thematic maps concern a particular theme or topic of interest. For example, while reference maps emphasize the location of geographic features, thematic maps are more concerned with how things are distributed across space. Such things are often abstract concepts such as life expectancy worldwide, per capita gross domestic product (GDP) in Europe, or literacy rates across India. One of the strengths of mapping and thematic mapping is that it can make such abstract and invisible concepts visible and comparable on a map.

It is important to note that reference and thematic maps are not mutually exclusive. In other words, thematic maps often contain and combine geographical reference information; conversely, reference maps may contain thematic information. What is more, when used in conjunction, thematic and reference maps often complement each other. For example, public health officials in a city may be interested in providing equal access to emergency rooms to the city’s residents. Insights into this and related questions can be obtained through visual comparisons of a reference map showing emergency room locations across the city to thematic maps of various population segments (e.g., households below poverty, percent elderly, underrepresented groups).

GIS Overlay Process

Within the context of a GIS, we can overlay the reference map of emergency rooms directly on top of the population maps to see whether access is uniform across neighborhood types. Of course, there are other factors to consider when looking at emergency room access (e.g., access to transport), but through such map overlays, underserved neighborhoods can be identified. Both reference and thematic maps are static or fixed representations of reality when presented in hardcopy format. Such permanence on the page suggests that geography and the things we map are also fixed or constant in many ways. This is far from reality. The integration of GIS with other forms of information technology like the Internet and mobile telecommunications is rapidly changing this view of maps and mapping and geography.

The diffusion of GIS and the popularity of online mapping tools and applications speak to this shift in thinking about maps and map use. In this regard, discussing the diffusion of dynamic maps is worthwhile. Dynamic maps are simply changeable or interactive representations of the earth. Dynamic mapping refers more to how maps are used and delivered to the map user today (e.g., online, via mobile phone) than to the map’s content. Both reference and thematic maps can be dynamic, and such maps are an integral component of any GIS. The critical point about dynamic maps is that more people, not just GIS professionals, can access such maps.

Unlike a hardcopy map with features and elements that users cannot modify or change, dynamic maps encourage and sometimes require user interaction. Such interaction can include changing the scale or visible area by zooming in or out, selecting which features or layers to include or remove from a map (e.g., roads, imagery), or even starting and stopping a map animation.

Just as dynamic maps will continue to evolve and require more user interaction in the future, map users will demand more interactive map features and controls. Furthermore, as this democratization of maps and mapping continues, map users’ geographic awareness and appreciation will also increase. Therefore, it is critical to understand maps’ nature, form, and content to support the changing needs, demands, and expectations of map users in the future.

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