About GIS?

What is GIS?  Geographic Information Systems (GIS) combines layers of information about a place to give you a better understanding of that place.  What layers of information you combine depends on your purpose -- finding the best location for a new store, analyzing environmental damage, tracking customers, tracking assets, viewing similar crimes in a city to detect a pattern, and so on.

Why use GIS?  GIS allows us to view, understand, question, analyze, and visualize data in ways simply not possible in rows and columns of a spreadsheet. For example, many datasets can have a spatial reference, including billing databases, customer list, marketing surveys, and demographic data.  The real power of GIS is its ability to integrate these common databases with a spatial reference. 
What are the benefits of GIS?
Custom Mapping Data Integration
Map Updates Spatial Analysis
Reveals Patterns & Trends Facilitate Planning
Cost Savings Improve Data Quality
Increasing Data Access Data Archiving
What data do you use in a GIS? (Vector / Raster)
Geographic Information stored as points, lines, or polygons are considered vector datasets while matrix or cell data are raster datasets.  In a GIS these features are categorized separately and stored in different map themes or overlays. 
Examples of Raster Data:
(Grids) Digital Elevation Models
 Raster
(Images) Orthophotography, Pictures, Aerial Photos
Examples of Vector Data:

(Lines) Streets, Water Mains, Sewer Mains  Vector
(Points) Manholes, Store Locations, Cell Towers
(Polygons) Sales Territory, Wetlands, Zoning Boundaries