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Maps and Attributes

Throughout this tutorial, we have presented photos and images of the Earth's surface and clouds, some accompanied by maps that locate, classify and describe objects thereon. All these objects share a common characteristic: they are visual, miniaturized representatives, or surrogates, of places and classes of features located geospatially on or above the surface, be it land or water. They thus depict aspects of the local, regional, or global geography, which we can locate geometrically in an x, y (horizontal), and z (vertical) plot. We can reference the plot, then, to some form of coordinate and projection system. A map projection is a specific way of transferring points or locations from a spherical globe onto a scaled-down flat surface (the map) according to a systematic, orderly realignment, using a latitude/longitude grid network.

Photos (images) and maps are inherently two-dimensional or planimetric, although we can use techniques, such as contours or shading, to present a quasi-three-dimensional appearance or to extract information about relative elevations above generalized datum planes. The most common type of three-dimensional map is the topographic map, which we already examined in Section 11. As we noted in Sections 10 and 11, maps in general nearly always have the following, essential information: graphic distance measures, scale, orientation and direction, projection type, and some geographic coordinate system, along with other descriptors and symbols in an accompanying legend. Topographic maps also have contour intervals.

15-1: What type(s) of map is/are the average citizen likely to encounter in everyday life? ANSWER

Maps are manmade derivatives of photos and images, designed to record information of various kinds about the spatial distribution of the specific categories of features present on the surface. We also refer to these categories as attributes, which are general descriptors that are inherently non-spatial (they depend on characteristics rather than the location). A parcel of land, regardless of size, likely contains a diverse mix of features or characteristics that we can assign to different categories; in other words, it has many attributes. A category can also be a theme. For instance, we may need a wide variety of thematic maps to fully describe the contents of a surface. Thus, given an area of, say, one square kilometer (or one square mile), one such map may display road networks, another vegetation cover, a third dwellings or functional buildings, a fourth engineering properties suited for excavation, and so forth. We may combine several themes on a multipurpose map, such as roads, buildings, recreational areas, etc. One common type of map shows land cover, which identifies an appropriate class or category that we may display within the map scale limits at selected points or locations. A variant of this map is the land use map that differs by detailing aspects of the cover involved in, or of interest to, human activities.

15-2: Think of (and list) at least four other types of specialized thematic maps. ANSWER

Examples of land cover or condition maps, each devoted to a single purpose or theme, appear here for slopes, soils, and vegetation, distributed over the southern part of Washoe County in western Nevada (the city of Reno lies near the center):

Examples of land cover maps over the southern part of Washoe County, Nevada.

These describe natural states of either the surface or materials underlying it. (Note: as we reduce these maps to fit the web page, information in their legends becomes too small to read. However, the importance of the illustration is in the differing patterns rather than the specific identifiers.) Much of the surface is undeveloped, but areas where people constructed buildings, in which to live, work, manufacture, or play, comprise one form of land use, as shown in this map.

Land cover map showing the distribution of constructed buildings in Washoe County.

15-3: Suppose you decided you wanted to live near Reno, but you are now residing in the eastern U.S. Your great Uncle has died and left you a piece of land. Explain how you could use the above 4 maps, even though "in absentia", to make an educated guess as to problems you might encounter in building a house, so you can start planning even before you get there. ANSWER

Some maps are composites of conventional, spatial distributions and graphs or other modes of data representation. Here is an example showing an area between Houston and Galveston, Texas, in which average monthly rainfall for the years 1965-67 at selected localities appears as bar graphs:

Composite map of the area between Houston and Galveston, Texas, showing the average monthy rainfall for 1965-67.

The Environmental Systems Research Institute (ESRI) assembled a comprehensive sampling of the many varieties of thematic maps for practical geographic applications on one of their web sites, accessed here ( Click on the list of fifteen application categories at the bottom of their home page to see some excellent examples.

* Parts of this section have been freely adapted from Activity (Chapter 7) of the Landsat Tutorial Workbook; that activity was prepared in 1981 by Mr. William J. Campbell, current Branch Chief of Code 935, the sponsor of the present Tutorial.

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Primary Author: Nicholas M. Short, Sr. email:

Collaborators: Code 935 NASA GSFC, GST, USAF Academy
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