GIS resources on the Web
January 27, 2006
5 years ago I needed to get maps and other GIS resources from contacts - men and women inside agencies where the data were developed.
Now many fundamental resources (maps and orthophotos registered for ArcView) and be downloaded free from State agencies and other universities.
The Ohio Department of Natural Resources maintains a digital data repository at http://www.ohiodnr.com/geosurvey/ogcim/petrol/petdig.htm - however, it is better to begin at http://www.ohiodnr.com/gims/ for shapefiles covering a number of themes. A search of various agencies turned up several sources of GIS information (often for a fee - except for internal use by that agency, even electronic downloads, something I do not understand as we taxpayers funded development of these resources in the first place and we are not in competition with these agencies).
Digital raster graphics for Ohio are found at http://oit.ohio.gov/SDD/ESS/Gis/data.aspx for free download.
Digital Orthophoto Quarterquadrangles (DOQQs) are available for download via an FTP site link. Each image is a quarter of a standard 7.5' quadrangle map. These are large files and only crazy data collectors download and save more than they really need for their projects.
Digital Raster Graphics (DRGs) are USGS topographic maps, scanned, rubber-sheeted and registered. Like the DOQQs, these are large files and only those with 160-Gbyte external hard drives (or their own servers with big data storage banks) have room for the whole collection.
I will go through the download procedure and point out some of the pitfalls that can waste a lot of your time.
For next time, please look for similar data dealing with another state. I have some old link information but discovered that Ohio' pages, bookmarked last year, are no longer valid. It took me a few minutes ( and various Google search terms) to find the right place. I suspect Matt will do Delaware. I already have Michigan, Iowa, Central America and California. Look for georegistered maps, orthophotos and other GIS information useful to ecological or geological investigators. I suspect most of Africa, Pakistan, Iraq, Iran, China, Russia and most other nations have virtually no digital data available free to the public (although the CIA probably does, but they are busy watching us, not sharing data with us).
It is important to look for metadata associated with each GIS resource downloaded. Particularly important are units and datum. This information is essential if you want to tie data from several different sources into a single view.
I will see if Global Mapper can be installed on some of these computers. Global Mapper can take raster data from one datum and convert it to another datum. A registered version is needed in order to export the result for use in your GIS. I have one registered copy and will investigate as to whether site license rates are available. You can probably download an examination copy for free (I do not know if permissions to install on these lab computers will allow you to) but exporting results so you can use them in ArcView takes a regi$tered copy.