Raster Data The Raster Data Model The Raster

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Raster Data

Raster Data

The Raster Data Model • The Raster Data Model is used to model spatial

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

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

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,

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

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 • 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

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 • Arc. GIS provides many tools for applying mathematical transformations to

Transforming Raster Data • Arc. GIS 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

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 Arc. Toolbox the DEM can

Transforming Raster Data • Using the tools in the Arc. Toolbox 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 • Arc. Toolbox also contains tools to convert from Raster Data

Converting Raster Data • Arc. Toolbox 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 • Arc. Toolbox provides tools for extracting Raster Data values to

Extracting Raster Values • Arc. Toolbox provides tools for extracting Raster Data values to vector data.

Creating Raster Data • Finally, there a number of tools in Arc. Toolbox that

Creating Raster Data • Finally, there a number of tools in Arc. Toolbox 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.