What is GiS?

1)   Introduction
A)  Q. What is a Geographic Information System?
A. Geographic Information System (GIS) is a computer program for storing, retrieving, analyzing, and displaying cartographic data.
Vector Spatial Location Data = X, Y, Z
Attribute Data Base = Data Information
B)  The Difference between Raster and Vector Maps
Maps in Geographic Information Systems are represented thematically. A standard topographic map will show roads, rivers, contour elevations, vegetation, human settlement patterns and other features on a single map sheet. In a GIS these features are categorized separately and stored in different map themes or overlays. For example, roads will be stored in a separate overlay. Likewise, rivers and streams will each be stored as a separate theme. This way of organizing data in the GIS makes maps much more flexible to use since these themes can be combined in any manner that is useful. The following illustration shows conceptually how maps are stored as themes in a GIS.
Each different theme is stored on a separate overlay. The overlays on the left represent a vector based GIS, where the information is stored as a series of points, lines and polygons. The overlays on the right represent a raster based GIS, where the information is stored as a series of discrete units called cells.
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C)  The Relation between Vector Spatial Location and Attribute Data Base
 Each Spatial Layer is consist of many Spatial features  Each Spatial Feature consist of many vertexes (x, y, z)  Each Spatial Layer is related to one Attribute Data Base Table  Each Spatial Feature is related to one Attribute Data Base Record  Each Record consist of many fields (up to 255)
D)  GIS Shape File types 2D & 3D (Point – Polyline – Polygon)
 Shape file contain spatial Location data of each feature Which are:- o Type  2D & 3D (Point – Polyline – Polygon) o Number of Parts o Number of Vertexes o X,Y, and Z of each vertex  Dbf file contain Attribute Data  o Each Attribute Data table consist of many records o Each record consist of many fields (up to 255)  Shx file is a relation file between the Shp file and Dbf fie  Point Layer consist of one vertex per Feature(x, y, z)  Polyline Layer consist of many vertexes per Feature  Polygon Layer consist of many vertexes per Feature and closed