We thank our colleague Kathy Hart, Head of the Research Access and Collection Development Section in the Geography and Map Division at the Library of Congress for this post, which was originally published on the Worlds Revealed blog. Many of the considerations and strategies described in this post also pertain to selecting maps for use with students. Find additional teaching ideas in these additional posts about teaching with maps; to focus student engagement and thinking, select questions from the Analyzing Maps Teacher’s Guide.
Libraries and museums often feature maps and related geographic content in digital and analog, large or small exhibits, displays and workshops. When considering the variety of materials available, how does one select the material that will best inform and inspire the visitor? The following are some factors to consider.
The primary factors are the place, theme and time period
All maps (except for imaginary places) represent a place on the earth. Many exhibits will have a specific geographic theme or focus, and for those, the starting point for map selection is fairly straightforward. If the display is focusing on a small geographic area such as a city, it may also be helpful to consider including maps showing a broader perspective, such as a state or country map, to give context to the place.
For some exhibits, a topical theme is the primary focus. In those cases, the place may be irrelevant, and thus, a selection of a variety of places (such as different cities or countries, etc.) is suggested. This variety will help connect your resources to your audience.
All maps represent a place at a given time. However, as with the place, the time period may or may not be critical to your selection decisions. If time period is not a factor, a selection of various time periods may enhance the exhibit or workshop. The date or time period of modern maps is shown in a copyright or other date information printed on the map itself. Older, historic maps will not always include a date of production, but an estimated date will be given in the catalog record. Some maps are created to represent a time period in the past (called a ‘date of situation’). These are ‘historical’ maps, as distinguished from ‘historic’ maps, the latter being produced contemporaneously in the past. To represent change over time, multiple similar maps, with differing dates, should be selected. Worth noting is that place names and boundaries change over time and are an interesting discussion point to promote comprehension.
Other factors are also important to your selection consideration
Visual interest and readability
The selected maps should be understandable, readable, and generally visually interesting. Consider the lettering or font style, use of color, understandable legend, and other aesthetic aspects. These aspects are often in the eye of the beholder, however, are important considerations which support the understanding and comprehension, particularly with a young or general audience.
While English is typically the default for a general interest display, exhibit or workshop in the U.S., it is important to remember that maps are produced in numerous countries and languages. Libraries or museums with extensive collections, such as the Geography & Map Division, contain a wide range of non-English language maps. Depending on the selected theme, geographic location, intended audience as well as the goals of the exhibit/workshop, a broad selection of maps in languages other than English may extend the appeal, and particularly connect with international visitors. Separately, another factor to consider is that the language may also present a nationalistic bias which should be considered in the selection decision.
Bias / perspective
Maps represent a point of view of the cartographer, publisher, or person/organization that commissioned the survey or mapping. The mapping agency or cartographer has a certain perspective that guides the creation of the map. They can create content that supports their intended message, whether to establish land claims, encourage business to relocate to a city, highlight environmental impacts, or numerous other reasons. For example, maps made by individual railroad companies in the 19th century, such as the one seen below, were highly propagandist. On the other hand, not every detail can be presented on a map, so mapmakers have to determine which concepts to include and which to omit. Depending on their goal and intended audience, there may be significant omissions. It is useful when selecting maps to exhibit to consider if the absence of specific details are problematic or contrary to the goals of the display/exhibit.
Data sources / data generalization
The subject matter shown, particularly on scientific maps, are based on numerous data points, and as such, have to be classified and generalized into some number of categories. For example, rainfall data may be collected by the minute or hour, however, the cartographer would decide, based on the intent of the map, if the data should be presented as hourly, daily, weekly, monthly, or annually, or some other configuration. Another example is the difference in maps showing presidential election results by county compared to ones adjusted for population. The arrangement of data influences how the information is perceived and understood.
Map projection is the mathematical conversion necessary to convert a 3D sphere into a 2D flat plane. Some map projections are better for larger, small, or other areas, however, map makers select a projection which will minimize distortion in one of four factors: land shape, distance, direction, or area. As an example, for a map of the world, with the commonly used Mercator projection where the lines of longitude and latitude are straight, Greenland, for example, will appear very large. By comparison, the Robinson projection uses curved lines of longitude, and better retains the overall shape and size of the continents on a world map. The USGS has a chart which describes the various projections. While consideration of projection is a minor factor in displays, the inclusion of maps with a unique or different projection provides an interesting variation and could increase the audience’s interest and understanding.
The scale of the map reflects the ratio of the distance of the earth to that which is shown on the map. The scale is the extent that the map is “zoomed in” or “zoomed out.” The scale may be noted textually, with a fraction, or graphically (a bar) on the map itself and will be stated in the catalog. A large scale map will show a city, county or other smaller area and may include many details. For example, a USGS topographic map has a scale of 1:24,000, which means that one inch on the map is equal to 24,000 inches in the real world. By contrast, a small scale map may show the world, a continent, or a large nation, for example, “Scale 1:30,000,000. 1 cm. = approx. 300 km. (186 miles).” The small scale map will provide fewer details and those will be generalized. In selecting maps, a consideration of scale should be based on the level of detail to show.
Other cartographic formats
Beyond print maps, globes and atlases are common and are important formats which convey geographic information and range in subject, time period, and language. When combined with print maps, or alone, they can greatly support the instructional objectives of the exhibit or workshop. Cartographic resources can also be found on cloth, wood, plastic, puzzles, playing cards, Japanese scrolls, and many other forms, all of which are included in the Geography & Map Division’s extensive collections.