Hey guys,
I'm new to the site, and I noticed that a majority of the state topo maps are available and more are coming out every day. I was just curious to know if anyone was working on a Virginia Topo map?
I can't say thank you enough to those who have put in their time to make these maps available to the rest of us.
I completed VA & 7 other eastern States a few weeks ago, but have not made them available because a large percentage (14% for VA) of the NED/DEM (grided elevation) data we get from USGS to build the contours is of an early vintage and seems not to correspond well with the contour lines as shown on the printed USGS topo maps. I have not come to a decision about what to do about this, but I am sure a caution to potential users would go unread.
Your, Oz, boyd, others comments?
How far off are we talking, probably 10s of feet right?
Correct. In places it does not look like the contours are describing the same piece of land. I have only compared about 50 7-1/2' quads with their DRG images, so would not say all 1000+ quads with DEMs produced by the earliest two methods would yield such results.
I personally wouldn't release it. But maybe smoke68 wants it anyway...
I am considering a partial topo map; no contour lines in areas were the DEMs are from the early production methods. But this is behind the WV transparent 10 foot contours from 1/9 arc sec (3 meter) NED data; CO with CIs as on the published 7-1/2' quads with NHD hydro and Federal land ownership, and an AK topo with NHD hydro. Also, since USGS just pulled the NED data produced by Camera Correllation in 2007 and replaced it with the traditional type DEM data, AR might need a redo (finished downloading the files earlier today). Wonder if they will pull northern IN, as that type of source data was also used there.
You guys are talking way over my head. It sounds like you have access to 2 different sources of topography data, and they don't match up in certain areas. Personally, I've seen several instances of USGS Quadmaps being incorrect with regard to stream flow routes, road locations, etc.
Whatever you decide, don't do it on account of me. I live in MS and sometimes go back to where I used to live in southwest VA to hike/camp/canoe. I'll make it either way, and it's not like I would use the information daily. I have, however, used the MS topo quite a bit, and it is AWESOME! I have Garmin's Topo DVD, and I might as well throw it away. 50 ft. topo lines just don't tell you much when there's only 30 ft changes within 10 miles.
Also, I have only figured out how to load the maps with installers. I haven't been motivated yet to utilize the overlay images on their own. If it was me making the map, I'd probably want to work on it till I got it right. No hurry.
Again, THANKS!
Not really 2 sources of topo data, just that each 7-1/2' quad is done independently of those surronding it with the best source data available at that time. The routines used to created the gridded data have evolved/improved through time. The early methods just do not appear to give a good representation of the contour lines as shown on the printed topo maps (and probably the gridded dataset was never intended to be used for contouring).
Quote from: -Oz- on April 02, 2009, 07:25:42 PM
I personally wouldn't release it. But maybe smoke68 wants it anyway...
Wow -- just the discussion I was looking for. :)
I just spent several hours looking for VA topos & came up with virtually nada. I'd like to get used to my new 60CSx (before an upcoming New Zealand trip) by practicing around my neck of the woods...
I live in Linden, VA, and do most of my hiking in the Northern Shenandoah valley. The area I would be most interested in would encompass Shenandoah Nat'l Park & all points west of it until the WV border was reached. No further south than say Harrisonburg & Waynesboro necessary, although the farther south the better. No further north than Winchester needed, and no further east than Rt 522, which parallels SNP on the east side.
Would you consider making this "sub-section" available in some way? I'm very familiar with the trails, so I don't need dead-on accuracy from a safety p.o.v. I would just be using it to get conversant with my GPS, MapSource, and determining the proper methods for setting up routes & tracks. Does your topo show hiking trails?
Anyway -- I'm a complete noob here :-[ so forgive me if I've suggested something that's prohibitively time-consuming or technically impossible.
John
An area with 39.25 on the north, 38.00 on the south, 38.00 on the east and somewhat into WV on the west would be about 33Mb and contains about 9 7-1/2' quads with poor contours (from early vintage USGS elevation data).
Not many, if any, trails as that info comes from the Census. The info on trails in the public domain is of a local nature.
You would need to use MapSetToolKit (free) to get the files into MapSource, or SendMap2 to create an gmapsupp.img (only one allowed on the GPSr) for the GPSr.
Email me an email address, and I will try to put something together later today or tomorrow and send it to you via USendIt.
At the rate USGS is updating the data, it might take 4 or 5 years before all the DEMs produced with early type production methods are replaced.
Quote from: maps4gps on April 04, 2009, 09:46:12 AMEmail me an email address, and I will try to put something together later today or tomorrow and send it to you via USendIt.
Thanks, that would be wonderful! I can't "see" your e-mail in your profile, but mine is trtlrock at comcast dot net.
Thanks, John
I have not tried that comparison.