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Data Formats



There are three major formats in which GIS-usable data can be obtained. They include hardcopy/eye-readable format, analog image format, and in fully digital format. Unique types of information can be accessed from each of these data formats.

Hardcopy (Paper, Linen Or Film)/Eye-Readable

Hardcopy maps are easily accessed from a wide variety of organizations. Hardcopy maps, as a form of GIS source data, can be digitized on a digitizing tablet into vector GIS format, or scanned and then converted into raster GIS format. Although there are potential accuracy problems which are associated with paper and linen maps (related to distortions due to shrinkage/expansion of the media) in capturing geographic features, there is still much unique geographic data which can only be found on these maps. An example of unique data from paper or linen maps is seen when seeking geographic data for a certain time period. Much of the digital data which is readily available may only be the most current, updated data for a region. For example, in order to find geographic data from before 1970, the only choice may be to access a paper or linen map. Use a film copy of the source document where available as this will be the most stable media.

Accessing dated tabular information for the development of an attribute database may be a similar endeavor requiring the use of paper documents. Organizations which have been in existence since before the dawn of digital filing systems all had to keep their data in paper "hard-copy" format at one time. Some of these older records may have been converted into digital form at one point. In other cases, there may be hard-copy documents which are the only versions of dated material. In order to conserve space and the integrity of most documents, many might possibly have been copied onto microfiche.

Image (Picture)

Aerial photography is found to be an abundant geographic data form. Photogrammetry (aerial mapping) is a common way of creating an accurate and up-to-date land base. Aerial photos provide the raw data which is necessary for various planimetric and topographic mapping applications. Photographic images are a very rich data source in that many geographic features can be seen clearly on a photograph but may not be seen in a paper map or a vector digital file (e.g., a large clearing within a wooded area would not be differentiated on most paper maps, but it is clearly visible on the aerial photo).

Aerial photography is available from many sources (i.e.: USGS, DOT, County agencies, etc.) The federal government has recently developed the National Aerial Photography Program (NAPP) in which states that desire to have their counties flown may split the cost with the Federal government. Many useful products are derived from the NAPP including 1:12,000 hard or soft-copy orthophotographs. An orthophoto is a scanned aerial photograph which has been digitally rectified using control points and a digital elevation model. The digital versions are especially useful for GIS applications. If the type of digital aerial photography needed is not available, organizations can create a request for proposal to solicit bids for aerial mapping, although this can be very expensive.

Digital

Within the digital format genre, there are many different varieties of data available.

These various options are becoming as numerous as what is currently available in paper maps. In terms of map graphics, there are again two different data structures which are quickly integrated into today's GIS systems: these are raster and vector data formats. Tabular data can be found in digital data format most frequently. Various forms of digital spatial data which are currently available in raster format may include some of the following: Scanned maps and aerial photography

Satellite Imagery
Digital Orthophotography
Digital Elevation Models

Some of the various forms of digital spatial data which are currently available in vector format may include some of the following:

Topological vector linework
Non-topological vector linework
Annotation layers


Some of the various forms of digital attribute data which can be input into a GIS includes file types associated with various software components: spreadsheet, database and word-processing. Some of the file formats which can be utilized include: dBase, Excel, and ASCII delimited text.

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