Data
creation
Modern GIS technologies use digital information, for which
various digitized data creation methods are used. The most
common method of data creation is digitization, where a hardcopy
map or survey plan is transferred into a digital medium through
the use of a computer-aided drafting (CAD) program, and georeferencing
capabilities.
Relating information from different
sources
If you could relate information about the rainfall of your
state to aerial photographs of your county, you might be
able to tell which wetlands dry up at certain times of the
year. A GIS, which can use information from many different
sources in many different forms, can help with such analyses.
The primary requirement for the source data consists of
knowing the locations for the variables. Location may be
annotated by x, y, and z coordinates of longitude, latitude,
and elevation, or by other geocode systems like ZIP Codes
or by highway mile markers. Any variable that can be located
spatially can be fed into a GIS. Several computer databases
that can be directly entered into a GIS are being produced
by government agencies and non-government organizations[citation
needed]. Different kinds of data in map form can be entered
into a GIS.
A GIS can also convert existing digital information,
which may not yet be in map form, into forms it can recognize
and use. For example, digital satellite images generated
through remote sensing can be analyzed to produce a map-like
layer of digital information about vegetative covers. Another
fairly developed resource for naming GIS objects is the
Getty Thesaurus of Geographic Names (GTGN), which is a structured
vocabulary containing around 1,000,000 names and other information
about places.
Likewise, census or hydrologic tabular data
can be converted to map-like form, serving as layers of
thematic information in a GIS.
Data representation
GIS data represents real world objects (roads, land use,
elevation) with digital data. Real world objects can be
divided into two abstractions: discrete objects (a house)
and continuous fields (rain fall amount or elevation). There
are two broad methods used to store data in a GIS for both
abstractions: Raster and Vector.