GIS Basics




In a GIS all of the features have information.  The information about the Centre County polygon is to the left. 


This table contains the demographic data, but it could also contain information on crime or politics related to Centre County.







 One of the advantages of a GIS is the ability to combine data from many resources—layer many themes.




This is a point theme of surface water supplies.




This is a line theme of rivers.




This is a polygon theme of the Pennsylvania county boundaries.



This example shows all three different themes can be layered into one.


Next is a demonstration of how to query the different data layers.






This is an example of a query.


The question is , What are the Surface Water Intakes that are within .5 miles of a river.




The features highlighted in yellow are all the points that are within .5 miles of a river.




When the surface water intake point is measured it is .33 miles from the river.