One of the things you may to to look at is the "Vermont GIS Basemap"
described in this newsletter

 http://www.vcgi.org/commres/publications/newsl_feb2006.pdf

and available at

 http://www.vcgi.org/dataware/?keyword=VGIS_BASEMAP

As far as I can tell, its a metadata file that points at a web
server that shows a "basemap" (including orthophoto) of VT.

The idea is that you get a file, say
"VT GIS Basemap.lyr" (which is an ESRI "layer" file),
open it up with ArcMap 9.1, and then the program
uses the info in the file to go over the internet
to show the part of the state you're zoomed in on.

Then you add your own layers (like our trails) on
top of that.

Looks like this is free, but you don't actually have
the data itself to work with offline.

Anyway, probably something else that would be worth
looking at.

I've pasted some of their "description" below.

 Jim M.


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Description: The "VGIS_BaseMap" (VT GIS Basemap) product allows users to
get a GIS basemap of Vermont without actually downloading any data
(including 1 meter color imagery!!!). Its a Web Map Service (WMS) which
can be viewed using one of the following products:

Software Requirements (one of the following)

    * ESRI ArcMap 9.1+
    * ESRI ArcReader 9.1+ (free download from ESRI)
    * ESRI ArcExplorer 9.1+ Java Edition (free download from ESRI)
    * Other clients which can view OGC Compliant Web Map Services (eg: Gaia)

Files:

   1. VT GIS Basemap.lyr = ESRI ArcMap 9.1+ "layer" file.

   2. VT GIS Basemap.pmf = ESRI ArcPublisher 9.1+ file, 
                           which can be read using ArcReader 9.1+.

   3. VT GIS Basemap.axl = ESRI ArcExplorer 9.x Java Edition file, 
                           ArcReader 9.x Java Edition

   4. VT GIS Basemap.gsf = Gaia 2.0.1+ session file.

---------------------------------------------------------

List of open source stuff

 * http://www.opensourcegis.org/ 
   a list of Open Source GIS applications
 * maptools.org (also hosts fwtools.maptools.org)

---------------------------------------------------------

 http://en.wikipedia.org/wiki/Open_Geospatial_Consortium
 OGC defines
   WMS - web mapping service
   ... and some other acronyms

  ...mostyl using REST : Representational State Transfer
     http://en.wikipedia.org/wiki/REST

 http://www.opensourcegis.org/

 Since the advent of google earth, other XML GIS types include
  KML (viewpoint spec for Google Maps, can include images & links, *.kml)
  KMZ (zip archive, *.kmz)
 as well as the older
  GML (GIS Markup Language)

 GeoTools - open source Java GIS toolkit is an implementation of OGC
 * http://docs.codehaus.org/display/GEOTOOLS/Home
 a java library for interacting with OGC data and servers.


-----------------------------------

 * GDV Client - javascript mapping client, it says;
 http://www.gdv.com/webmapping/umn_client.php
 ... but I didn't see it do anything interesting.

 * intermap - java UVM client, it says
 ... ditto

 * uDig - "An open source viewer/editor that brings together internet,
           database, and file-based spatial data."
   http://udig.refractions.net/confluence/display/UDIG/Home

   Looks pretty stable and cool.
   under New Project: 
    import a "Web Map Server"
    import a "Web Feature Server"
    and wants the URL for its "GetCapabilities" document.
  
  I'm not sure that the VT folks have set one up, though...

---------------------------------

somewhat off topic - photogrammetry
(converting pictures into data)

 e-foto
 http://www.efoto.eng.uerj.br/index-en.html
 educational tool for photogrammetry

---------------------------------

also somewhat off topic - computer vision library

 http://www.intel.com/technology/computing/opencv/index.htm
 "Aid commercial uses of computer vision ... by providing
  a free and open infrastructure where the distributed 
  efforts of the community can be consolidated..."