Smithsonian National Museum of Natural History, North American Mammals
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Maps are used throughout this site, and though they may all look alike, there are two quite dissimilar types being used. One is the static map used to depict each species' geographic distribution. The other is a dynamic and interactive map operating in a Geographic Information Systems environment, or GIS.

Species Maps

There are different methods for portraying the extent of a species' occurrence over a geographic area. One way is to map only those areas where the species occurs. Such maps attempt to closely reflect both the actual areas where a species does occur, and the adjacent unsuitable habitats where a species does not. In Colorado, for example, the Uinta chipmunk occurs only between 2,135 m and 3,447 m elevation, whereas the Colorado chipmunk living in the same area exits only at or below 2,135m. Those elevation differences would be reflected in a map showing only the areas of species occupancy. Very accurate data are necessary to make such fine distinctions, and this information is not always available.

A second type tries to encompass all individuals of a species with an imaginary boundary. While the first type defines areas of occupancy, the second type defines a species' geographic extent, yet without indicating where within the boundaries individuals are likely to occur. Most maps used on this web site define the geographic extent of a species. A few better reflect the areas of occupancy. Both methods are visual presentations of scientific data.

Species do not know they have been mapped, and both their numbers and locations can change over time. Weather patterns, catastrophic events, and long-term climate changes may effect the distribution of plants, which in turn influences the abundance and distribution of mammals. Animals move, and mammals move very well, by land, water, and air. So it is that vagrants travel beyond the boundaries set by species range maps, states, and nations. All these factors, and more, speak to the accuracy of the maps. Each map represents a best estimate for areas where species occur, and may not depict the precise locations where they occur.

GIS Map (Geographic Search)

Illustration of GIS Search

The map of North America is a true GIS map delivered from a GIS-dedicated server. What makes it GIS is the fact that it is smart. As a smart map, it is linked to different sets of data, such as the species maps, locations of political borders, rivers, cities, parks, etc. Essentially, this GIS map consists of over 400 maps layered into one. Also, being an interactive map means you may ask the map a question. We have set the map to answer the general question, "Which species of mammals occur at this location?" "This location" is wherever you choose to mouse click on the map. In a very real sense, the mouse click sends a probe down below the skin of the map through the more than 400 underlying layers (see illustration). Whenever the probe passes through the range on a species map, that species is recorded and listed along with every other species encountered by the probe. That is how an answer is determined for each question, and the result is known as spatial analysis.