List of Public Domain Data Sources

[Seldom]

I'm new to this group, so it may already exist, but it would really be nice to have a list of links to public data sources. The obvious ones are NHD, GNIS, USDS Seamless, NPS DataStor, etc.....

Trails data, however, is really hard to find, as is vector data for ground cover.

[Seldom]

Thanks, that's what I'm doing.

Download the groundcover from USGS Seamless. 
Use Photoshop to generate edge traces for forest types.
Export those to Illustrator.
Export Illustrator to DXF. Load DXF into GM. 

So far, 1 or 2 hours spent making coffee and watching the box. 

After I've saved it as a GMP file I spend around a day selecting areas inside of areas and making islands from the inner areas.  That gets me the southwest corner of Utah.

Any tips would be appreciated.

[maps4gps]

I did a 'test' on this in the spring of 2008 and it took a good 1/2 day of interactive editing to process the 'forest' cover for a 1x1 degree area in CO.  Closing the line boundaries along the 'quad' edges so GM can make polygons and then editing the enclosed open areas and 'clumps' of trees withing them takes most of the time/effort.  

Wish someone would write a free utility program to process such data.

I have the 2001 NLCD downloaded.  USGS is currently working on a 2006 version, but may be another year or two before it is available.

[Seldom]

How are you getting your DXF? When I generate the DXF as described above they come into GM as polygons.  The GM import takes hours, but then I save them as a GMP and things speed up a lot.  I've been selecting deciduous and conifer forest colors in Photoshop with the "Select Color Range" menu to make the GM "Wooded Area".  Photoshop then generates a single polygon bounding the two colors and at the image edge.

I been selecting the areas in Seamless using the window, figuring that I could always split them up in GM.

I too would like your free utility if you ever find it, but it seems like it would be a bear to write.
List all the big areas with nothing around them, create sublists of all the little areas for each big area, subtract all the sublists from their big areas.

[maps4gps]

My 'test' procedure with the software I have was:
In Photoshop Elements -
    change the 13 non-forest types to white (12 as ice is white)
    change the 3 forest types (deciduous, evergreen & mixed) to black
    save as tiff file and copy .aux, .prj and .tfw files to this name
In GM - 
    open tiff and export as raster/bill/grayscale 8 bit
    open bill as elevation - will be purple and blue with min elv = -1 and max elv = 0
    contour the data for a -0.5 value
    add line segments at the edges to 'enclose' the forest areas
    convert line data to area data - results unusable if error made in previous step
    create open area polygons withing forest polygons - mistakes can be recovered
    project to lat-long and trim to 'standard' quad size

With the data coming into GM as polygons, you are saving almost half the interactive processing time and the most error prone step to do manually.  I will have to see if PSelements can do the edge traces and export dxf.

In the one time I field tested the data, it did not seam to be too useful as the forest polygons were not that easy to distinguish and on jeep trails we either were in an extensive forest area or outside the forested area.  I would also expect a conflict with the green forest symbol polygons and the solid green symbol used for parks, etc. 
For CO, OR and DK users, I would expect the raster images to be more usefull as they would be more current and accurate.

[Seldom]

I know that Photoshop won't export the DXF.  It will export AI to Illustrator.  That exports the DXF. Still, if you can get Elements to export to AI, AI is a reasonably cheap translator, compared to Photoshop.  Too bad Mike never got around to making an AI export/import from GM.

I forgot to mention that once my DXF is generated I have to project it using the projection from the TIFF, and then generate a false northing/easting to get the DXF to overlay the TIFF.

[maps4gps]

Elements does not have an edge trace function (in version 4) - new versions may not either as it is designed for photographs not making illustrations.
Is the version of Photoshop you are using the full professional version?

[Seldom]

Yes, Photoshop CS3.  It's not too expensive if you can wangle an Academic Discount using spouses or offspring.

The selection is "Select Color Range".
The command is a button on the Actions tab, and it is called "Make Work Path from Selection"
The export is Export>Paths to Illustrator.

[Seldom]

I just found one drawback to the vectorizing process I described.  Sometimes polygon's are malformed, and can't be gridded.  The workaround looks like it will be to make the grid big enough to take the whole polygon.

[leszekp]

Moagu doesn't "vectorize" the data except in the coarsest sense of the word, so it doesn't keep attribute data. You could create a Moagu map from the NLCD raster data, but it's going to draw and pan very, very slowly.

Converting the map into KMZ format with minimal compression, and using it in a Colorado/Oregon/Dakota is probably the best approach.

If you can live with older data with a coarser categorization scheme, there's LULC data in shapefile format available for free:

http://www.webgis.com/lulcdata.html

[Seldom]

This is probably a fools exercise, but tThis is vectorized output from the process I described above:


Overall view of South Utah Wooded Areas-polygons only.


Same polygons overlaying the GEOTIFF from which they were derived.


Close Up with polygon overlaid.


Close Up without polygon overlaid.

The conversion uses Photoshop to select colors and export paths to Adobe Illustrator.  This I described above.  One thing I don't remember saying is that if GEOTIFFs are saved in Photoshop they lose all their projection info, so DON'T save your changes in Photoshop.

USGS provides the Tiffs in Albers Conic projection.  Photoshop and Adobe Illustrator don't understand it. So  the way I brought them in was:
Open the GEOTIFF in GM
Use GM to import the DXF I got from AI.  This could take several hours per DXF.
Re-set the false easting and false northing on the DXF projection.
Save DXF import as a GMP.  This vastly speeds up the reload time.

Once the alignment was correct, reproject to Geographic.

[maps4gps]

Nice work.

How big of an area (in degres) did you do?

Our software and process differ somewhat.  I used PS Elements to change the three forest types to black and changed everything else to white.  Saved as a TIFF file.  Copied the original .aux, .prj. and .tfw files to this new TIFF file name.  GM considered these four files a valid geotiff file and everything was registered perfectly.

[Seldom]

Thats two degrees North/South by 5 degrees East/West.  Gets nasty at the edges, because GM won't grid malformed polygons.  Malformed polygons have to overlap the edges, like the one at the top right of the overall view.  This is about a rainy day's work.  Most of the time spent making deleted islands inside of undeleted islands.

[maps4gps]

If I remember correctly, it took me 4-5 hours or more for a 1x1 degree area.  About 45% making lines at the edges to close the polygons, and 45% making clearings in the forest and smaller forest in the clearing.  Some of the forest polygons were so complex I was surprised GM was even able to make them correctly.

[Seldom]

If I remember correctly, it took me 4-5 hours or more for a 1x1 degree area.  About 45% making lines at the edges to close the polygons, and 45% making clearings in the forest and smaller forest in the clearing.  Some of the forest polygons were so complex I was surprised GM was even able to make them correctly.

This is a little late in coming, but while GM imports my DXF files perfectly, it is pretty erratic when it comes to gridding them into forest polygons suitable to map.  Neither mkgmap or cgpsmapper like some of those big polygons either.  mkgmap generates "Serious Error" messages and really ugly polygons.  cgpsmapper reports "Too big RGNtable" and quits.