This tutorial topic provides
information about the standards INSIDE Idaho uses for GeoData. It will help you understand
what GeoData formats are available on the site, how the files are named and compressed,
and what projections the data may be in.
Data FormatsVector data are provided in Environmental Systems Research
Institute (ESRI) shapefile format. Additionally, some data may also be found as
Arc/Info coverages.
Image data are provided in GeoTIFF, MrSID, and USGS native format.
Gridded data are provided in Arc/Info Grid format which requires ArcView with the
Spatial Analyst extension or Arc/INFO to view.
If you have a question concerning the data format of a particular data set, check the
"Digital Form" element of the "Distribution Information" section of
the metadata.
File Naming Convention
The naming convention most files adhere to is:
description_extent_source.tgz
| description: |
a maximum of 8 characters to uniquely describe the theme. |
|
| extent: |
a short identifier for the area covered by the theme (e.g.:
"24k" signifies the theme covers a 24k quadrangle whereas "id"
signifies that the theme covers the entire state of Idaho). |
|
| source: |
the data contributor. |
Example: counties_id_idwr.tgz
Compression
Compressed files are "archives" used for distributing files. They
contain one or more files within them. They make it easy to group files and make
downloading these files faster. Essentially, the compressed file is a container that
holds the data and delivers it to you (like a box from Amazon that contains several books)
Most data have been compressed into ".tgz" files--i.e. a tar file was created
and then compressed using gzip. This compression method was found to be friendly to
both UNIX and PC platforms while offering excellent compression ratios. Numerous
commercial and shareware tools for extracting data from .tgz files are available.
Projections
All data are available in Idaho Transverse Mercator (IDTM) projection.
Additionally, some data are available in Universal Transverse Mercator (UTM)
projection. A discussion of the IDTM and UTM projections can be found here. Parameters for
both projections can be found here.
Idaho is split into two UTM zones: Zone
11 (west of 114º W longitude) and Zone
12 (east of 114º W longitude). Data spatially organized by USGS 24k
quarter-quadrangle, 24k quadrangle, 100k quadrangle, or 250k quadrangle are projected in
their respective UTM Zone.
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