GIS Map Characteristics to Keep in Mind

Michael N. DeMers

Updated

2016-03-26 21:14:02

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GIS For Dummies

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Your GIS (geographic information system) is very handy and a great navigation tool, but what you see on the GIS screen isn't necessarily what the actual terrain looks like. As you use your GIS, remember the following facts:

Map Characteristic	What It Means
Maps are models — not miniatures	Maps generalize geographic features by using symbols so that all features will fit the specified output size.
Map scale has a huge impact on GIS analysis	Small-scale maps cover large areas with little detail, and large-scale maps cover small areas with lots of detail.
Maps are a flat model of a spherical earth	Maps use projections to compensate for the flat versus spherical issue, and each projection has its own type and amount of distortion.
Maps have a reference grid, or coordinate system	The reference grid helps you navigate the map and links the spherical earth to the map projection.
Maps have a reference starting point, or datum.	Datums are based on a model of the Earth called a reference ellipsoid and enable all the various projections in a GIS work together to give an accurate picture of the Earth.

About This Article

About the book author:

Michael N. DeMers is a Professor of Geography with more than 25 years of GIS experience. He is also CEO of DeMers Geographics, a provider of educational resources for GIS students and educators.

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