GIS (Geographic Information System)
Maps have been
used for thousands of years, but it is only within the last few decades that
the technology has existed to combine maps with computer graphics and databases
to create geographic information systems or GIS.
Geographic information system:
A Geographic Information System or Geographical
Information System (GIS) is a system designed to capture, store, manipulate,
analyze, manage, and present all types of spatial or geographical data.
Geographic Information Systems is a computer-based tool that analyzes, stores, manipulates and
visualizes geographic information, usually in a map. In other hand, we can say
it is a system that collects, displays, manages and analyzes geographic
information.
The key word to this technology is Geography – this means that
some portion of the data is spatial. In other words, data that is in some way
referenced to locations on the earth.
Coupled with this data is usually tabular data
known as attribute data. Attribute data can be generally defined as additional
information about each of the spatial features. An example of this would be
schools. The actual location of the schools is the spatial data. Additional
data such as the school name, level of education taught, student capacity would
make up the attribute data.
It is the partnership of these two data types that enables GIS to be such an
effective problem solving tool through spatial analysis.
Geographic Information Systems really comes down to just 4 simple ideas:
·
Create geographic data
·
Manage it.
·
Analyze it and…
·
Display it on a map.
GIS stores information about the real world as
thematic layers. Of course, these layers are all linked by their geographic
coordinates. As a result, we save cost because of greater efficiency
in record-keeping and can make powerful spatial analysis with
ease.
Geospatial data is created, shared, and stored in many different formats. The
two primary data types are raster and vector. Vector data is
represented as either points, lines, or polygons. Discrete (or thematic) data
is best represented as vector. Data that has an exact location or hard
boundaries are typically shown as vector data. Examples are county boundaries,
the location of roads and railroads using lines, or point data indicating the
location of fire hydrants.
Raster Formats:
By contrast, raster data is best suited for continuous data, or information
that does not have hard boundaries or locations. As raster’s, the data are
viewed as a series of grid cells where each cell has a value representing the feature
being observed. Think of raster data as appropriate for modeling surfaces like
elevation, temperature, precipitation, or soil Ph. These phenomena are measured
at intervals (think weather stations), and values in between are interpolated
to create a continuous surface. Raster data also includes remote sensing
imagery, like aerial photography and satellite imagery.
Vector Formats:
SHP: Shapefile
The ESRI Shapefile has become an industry standard geospatial data format, and
is compatible to some extent with practically all recently released GIS
software. To have a complete shapefile, we must have at least 3 files with the
same prefix name and with the following extensions: .shp = shapefile, .shx =
header and .dbf = associated database file. Additionally, we may have a .prj =
Projection file, a .lyr = layer file, and other index files. All these files
must be saved in the same workspace.
GDB: Geo database
The file geo database is a collection of geographic datasets of various types,
with the most basic types being vector, raster, and tabular data. There are
three types of geo databases: file, personal, and ArcSDE. Geo databases are the
native data format for ESRI’s ArcGIS.
GIS is more than just software. People and methods
are combined with geospatial software and tools, to enable spatial analysis,
manage large datasets, and display information in a map/graphical form.
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