GIS Basics


There are two types of geographic data models:


Raster: Grid



Below is a raster example of the National Land Cover Data Set.  This example is acquired by the Multi-resolution land characterization (MRLC) consortium.


Developed from LandSat Thematic Mapper Satellite Imagery and produced as a cooperative project between the USGS and the US EPA

National Land Cover Dataset


Raster data is a structure composed of rows, and columns.  Group of cells with the same values are used to represent features. This example below is zoomed in to the Harrisburg area. 




In this example, dark red is used to represent High Development, as in the case of Harrisburg, Camp Hill, and Mechanicsburg.  These cells have a value of 3.  Blue is used to represent water.   Cells that define the Susquehanna River have a value of 1.








Vector: Line



This is an example of Centre County (polygon) with streams (lines) and water usage wells (points).  All of these features have specific attribute information.