Raster Data

The Raster Data Model The Raster Data Model is used to model spatial phenomena that vary continuously over a surface and that do not have discrete dimension –Elevation –Temperature –Rainfall –Noise Levels

Surfaces Have Numeric Values Things like elevation, temperature, slope and precipitation have measurable values for any particular location on the earth’s surface.

Surfaces Have Numeric Values To model these phenomena, an area of interest is divided into an array of identically sized squares The centers of these squares then become the ‘sample points’

Surfaces Have Numeric Values The values of the variable of interest are recorded, or estimated, at each of the sample points.

Surfaces Have Numeric Values These values can then be assigned colors, or shades of gray, in order for them to be visualized

Digital Photos The most familiar type of Raster Data is the digital photograph. Digital Photos are raster datasets that record the relative amount of light being reflected off of a surface.

Color Digital Photos Color Digital Photos are actually made up of three Raster Datasets, each of which describes the amount of reflected Red, Green & Blue light, respectively. These 3 raster datasets are combines (by the computer) into the R-G-B color image we are used to seeing.

Transforming Raster Data ArcGIS provides many tools for applying mathematical transformations to Raster Data. Many of these transformations take advantage of Map Algebra, a special set of functions similar to Matrix Algebra.

Transforming Raster Data For Example: You might start with a Digital Elevation Model (DEM), which contains the elevation values at regular intervals.

Transforming Raster Data Using the tools in the ArcToolbox the DEM can be used to calculate a Slope Raster. This Slope Raster contains the Maximum change in elevation for every elevation point, measured in degrees.

Converting Raster Data ArcToolbox also contains tools to convert from Raster Data to various types of Vector Data. Including: –Topographic Contours –Polygons of “Classes” of values that occur in the raster dataset

Extracting Raster Values ArcToolbox provides tools for extracting Raster Data values to vector data.

Creating Raster Data Finally, there are a number of tools in ArcToolbox that allow one to Create Raster Data. For example, you can create a Raster Dataset that contains the Distance from some feature to every other point in the area of interest. The distance values can then be extracted to other datasets for use as an attribute for analysis.