Alluvial Fan-fan-shaped wedges of sediment that extend from a mountain front or steep escarpment onto an adjacent lowland. Alluvial fans are formed by sediments that are transported from uplands by streams or rivers. Click to view an aerial photograph of one of the alluvial fans in the Marana Community.

ARC/INFO-server based hybrid GIS software package, written and marketed by Environmental Systems Research Institute (ESRI). Comprised of Arc, the spatial GIS component and Info, a relational database, although ArcInfo can also be linked to external databases such as Oracle. ArcInfo, unlike the more user friendly ArcView, has a steeper learning curve. A number of add-on extensions are available for example, TIN, GRID, NETWORK and COGO, which provide additional functionality.

ArcView-desktop GIS software package written and marketed by Environmental Systems Research Institute (ESRI). Cheaper and easier to use (but less powerful) than their original system, ARC/INFO, ArcView has become well-established as one of the world's most popular desktop mapping packages. Windows based user interface means that novice users can be quickly taught to manipulate analysis and graphical tools. Can be linked to ARC/INFO database files and can handle both vector and raster data types through the addition of extensions.

Aspect-the direction in which a slope or surface faces, especially in the context of exposure. Aspect can be calculated by many GIS, and is usually expressed in degrees relative to North. For example, North is 0 degrees, and South is 180.

Attribute-a trait, quality or property describing any point, line, or polygon.

Attribute Table-a tabular file containing rows and columns. Attribute tables are normally associated with a class of geographic features. Each row represents a geographic feature. Each column represents one attribute of a feature, with the same column representing the same attribute in each row.

Buffer-In spatial information systems a buffer zone, or simply buffer, is a polygon enclosing an area within a specified distance from a point, line, or polygon. Accordingly, there are point buffers, line buffers, and polygon buffers. Buffers are useful for proximity analysis, for example, finding all stream segments within 300 feet of a proposed logging area.

Caliche-a subsurface soil horizon composed of cemented calcium carbonate precipitate. Caliche layers are compact and impermeable; they impede the movement of water downward through the soil and retain moisture at shallow depths.

Contour Line-a set of points representing the same value of a selected attribute and forming an imaginary line. The term contour, or contour line, is most commonly used for lines connecting points on the ground having the same elevation.

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.

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.