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GIS - Geography Information Systems

Geography Information System Data

Spatial Data: Spatial or coordinate data represents features with a known location on earth.
    Points:  X and Y locations
    Line:  Connected X and Y locations
    Polygon: connected X and Y locations that contain attribute information
    Raster: row and column matrix representing geographic space

Attribute Data: Attribute data are the information linked to the geographic features (spatial data) that describe those features.
    Attribute data are the non-graphic information associated with a point, line, or area elements in a GIS.

Data Layers:
Data Layers are the result of combining spatial and attribute data.
Data Layers are where we add the attribute database to the spatial location.

Layer Types:
A layer type refers to the way spatial and attribute information are connected.
There are two major layer types: vector and raster.
   
Vector
: Points, lines and polygons (spatial data) associated with databases of attributes (attribute data) are considered vector layer types.
   
Raster
: A row and column matrix (pixels) of X and Y space with attribute information associated with each pixel is considered a raster layer type.


Topology:
Topology is how and where geographic feature are related to one another.
Topology is the critical element that distinguishes a GIS from a graphics or automated cartography system.
It is essential to the ability of a GIS to employ spatial relationships. Topology is what enables a GIS to emulate our human ability to discern and manipulate geographic relationships.
   


Data Input - the creation of digital spatial data.
X and Y Coordinates
database entry
digitize paper maps and convert into digital file
scan paper maps so as to read spatial features in a rasterized format
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Data Management:
Spatial data requires unique maintenance issues to assure the usability of the data.
Errors in digitizing, data entry and in the original data must be considered along with the methods of data entry and the scale of the data digitized.

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One very cool feature of GIS is Digital Terrain Analysis:
This allows for interpolation from point data (elevations), derivation of slopes and their aspects, watershed computations and identification and construction of view sheds.
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GIS software programs are usually either vector or raster based with capabilities in using both layer types.

Vector Based Software:
-ArcView
-ArcMap
-MapInfo

Raster Based Software:
-Erdas Imagine
-IDRISI

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caveat: * I have knowingly scabbed this information from a variety of web published locations and have NO intent to use this info for any reason other than to educate myself on the topic of GIS. This information is not for reuse, nor use by anyone other than myself for the pure purpose of quelling my own curiousity.

email : kayakcraig@yahoo.com      page last updated : 07/2005



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