Working with Vector Data - Desktop GIS: Mapping the Planet with Open Source Tools - page 27

Joe Asks. . .
What Is a Shapefile?
A shapefile stores vector features and their attributes. A given
shapefile can contain only one type of feature: points, lines, or
polygons.
The term is actually a bit misleading, since a shapefile always
consists of at least three separate files. For example, a shapefile
named alaska would consist of the following:
• alaska.shp containing the spatial features
• alaska.dbf containing the attributes
• alaska.shx , which is an index file that allows random access
to features in the alaska.shp file
In addition to the three main files described here, you might
also find alaska.sbx , alaska.sbn , and alaska.qix files. These are
additional index files used by some applications. One last file
you'll often find associated with a shapefile is a . prj file. This file
contains the projection information for the shapefile, including
the geodetic datum (for more on datums, see the Joe Asks. . .
on page 140 ) .
If you are sharing a shapefile with someone, make sure you
include at least the . shp , . dbf , and . shx files; otherwise, it will be
unusable.
raster image of the earth (which we'll use in a later chapter when we
work with rasters).
Choosing a Viewer
Most of the applications in Appendix A , on page 269 , that work with
vector data go beyond a viewer. Let's use several of them to look at the
sample data. Of course, you don't need to use all of them, but following
along will help you decide which is best for you. For help on installing
any of the applications, see Appendix B , on page 290 .
The truth is that nearly all the OSGIS viewers use a similar user inter-
face. If you can use one, you can figure out the others. Let's start by
viewing the world borders data using the User Friendly Desktop Inter-
net GIS, uDig.