Intro to Rasters Extracted from the ESRI course “Working with Rasters”

Contents What’s a Raster (or Grid) Features vs Cells Resolution questions Structure Types of Rasters esf Laboratory for Applied GIS 2

Raster? Grid? Rasters may be categorized as one of two types: thematic rasters and image rasters. esf Laboratory for Applied GIS 3

Features vs Raster esf Laboratory for Applied GIS 4

Resolution Questions The output raster (Environment) should have the same (or larger) cell size as its inputs (a smaller cell size will NOT improve accuracy!). esf Laboratory for Applied GIS 5

Coordinate Systems Raster data has Three origins! esf Laboratory for Applied GIS 6

Types of Rasters Thematic –Discrete (categorical, discontinuous) –Continuous Image –Satellite –Aerial photographs esf Laboratory for Applied GIS 7

Thematic Rasters Represent objects that have definable boundaries, like buildings, wells, land parcels, lakes, etc. May represent a characteristic of features instead of the features themselves. May or may not have an attribute table (called a Value Attribute Table (VAT) esf Laboratory for Applied GIS 8

Continuous Rasters Data that varies continuously over the raster like elevation, pollution levels, noise, etc. esf Laboratory for Applied GIS 9

Image Rasters "image" usually refers to values that represent the intensity of reflected visible light or other radiation (infrared, etc.) Data may consist of one “band” (Panchromatic or simply Pan) or many bands (  Composite) esf Laboratory for Applied GIS 10

Composite Image esf Laboratory for Applied GIS 11 But this is Remote Sensing Stuff