Relief: refers to the changes in elevation that one experiences when moving over a landscape. High relief = large range of elevations (mountian range). Low relief = small range of elevations (flat plains).

Degree of Slope: a measure of change in surface value over distance, expressed in degrees or as a percentage. For example, a rise of 2 meters over a distance of 100 meters describes a 2% slope with an angle of 1.15.

This section contains tutorials (there are no questions to answer at this point) illustrating the different types of data layers and GIS commands that researchers commonly use. These tutorials were designed to introduce you to digital spatial data and provide you with a basic idea as to which types of research GIS can provide assistance.

Tutorial #1. DEM-Digital Elevation Model

A , or digital elevation model, is one of the most basic and important kinds of maps used in GIS-aided archaeological research. DEMs are digital representations of a geographic area's terrain; they carry data concerning an area's changes in elevation in an X, Y, Z coordinate system. You can think of DEMs as digital versions of USGS topographic maps, on which changes in elevation are expressed with regularly spaced , examples of which can be seen in Figure 2. Indeed, the majority of the DEMs available for areas within the United States were created by people who digitized contour lines directly from USGS 7.5 and 15 minute topography maps. Figure 2 is the composite of a number of USGS 7.5 minute topography maps on which site locations were plotted.

Select the theme named to view a DEM of your project's study area, the Northern Tucson Basin. includes information for the same area as does Figure 2. Note how this theme uses different colors to represent different zones or ranges of elevation. The Tortolita Mountains to the east, and the Tucson Mountains to the south account for the highest elevations in the area and, therefore, are shaded with the lightest color. Conversely, the Santa Cruz River and floodplain, which run southeast to northwest through the lower half of the area, have the lowest elevations and, therefore, the darkest shade of color in the theme. Compare to Figure 2 to orient yourself and to note the differences and similarities between the ways the two maps represent the same landforms.

To view a different version of this DEM, select the theme named . This DEM highlights terrain , as it would look from a plane in late afternoon (the sun is halfway down the western/southwestern sky). This theme is a product of the command in ARC/INFO and ArcView. The striking contrast between light and shadow accentuates the relief of the area and provides an informative and easily understood image. You may want to flip back and forth between and or compare them side by side to observe the similarities and differences between the two visual outputs of spatial data from the exact same geographic area.

Tutorial #2. Slope Maps

In addition to elevation, is also an important environmental variable to take into account in settlement pattern studies. GIS software use sophisticated mathematical equations to produce slope maps from DEMs. Click on to view a degree of slope map for your study area. Darker shades of color are steeper slopes and lighter shades represent areas that are flat. Compare to to observe which landforms correlate with areas of steeper slopes.

 

DEM: stands for digital elevation model. DEMs are digital topographic maps that carry data concerning the elevations of a geographic area.

Hillshade: an ARC/INFO and ArcView command that allows a researcher to accentuate an area's topographic relief by positioning a light source at any compass direction and altitude in relation to a DEM. For example, one could position the light source to mimic the rising or setting sun for any position on the globe.