Comments on: Public domain topographic maps?

Question: Public domain topographic maps?

ConstantineXVI — Tue, 30 Jun 2009 08:01:50 -0800

Is there somewhere that has the USGS (public-domain?) topographic maps available for free download?

I'm trying to set a friend up with a off-road GPS app (ViewRanger), and trying to get the topographic maps of the USA for it. I know that the USGS produces these maps, and (IIRC) since they're government-produced, the maps are public domain and therefore one can get them free. Is there anyone that offers these maps for free download? Even better, in a format that ViewRanger supports?

PS: I'm a total newbie to this, feel free to correct me on anything I got wrong

By: jessamyn

jessamyn — Tue, 30 Jun 2009 08:05:48 -0800

Yes. USA maps are available at the Internet Archive in TIF, TGW and FGD. Better searchable interface at Libre Map. Thank Jared Benedict (I bought Vermont!).

By: bumpkin

bumpkin — Tue, 30 Jun 2009 08:22:15 -0800

One stop shopping for all USGS products:

USGS National Map Seamless Server.

By: rmd1023

rmd1023 — Tue, 30 Jun 2009 08:51:36 -0800

... whoah. i totally forgot that i'd contributed to Jared's ransom until i saw my name on the "free the maps" page.

By: bink

bink — Tue, 30 Jun 2009 08:54:14 -0800

You can get PDFs of topo maps free at the USGS site.

By: aka burlap

aka burlap — Tue, 30 Jun 2009 11:01:19 -0800

I asked about topographic maps of Texas a few months ago and got a bunch of helpful answers.

By: elendil71

elendil71 — Tue, 30 Jun 2009 11:02:32 -0800

What everyone else has said for resources. You're ID doesnt specify where you are from but you could also run a search for GIS data (DRG's in particular - Digital Raster Graphics) by state. These are probably importable with the app you mentioned (and are almost always TIF's - sometimes labeled as TIFF's - just remove the last "F" and it will be recognized if you run into problems). These are usually whole scanned versions of the USGS maps which may or may not be seamless, and they are typically georeferenced in either UTM NAD 27 or, more commonly NAD 83. I would point out that the actual scanned maps, if they show UTM grids at all, are ALL in NAD 27 - the NAD 83 georeferencing convention is relatively recent.

Okay that's way more info than you need. Sorry. Got all GIS nerdy.

By: ConstantineXVI

ConstantineXVI — Tue, 30 Jun 2009 13:47:17 -0800

After a little back-and-forth with ViewRanger support, it appears they don't support third-party maps at all. Oh well, though I'll probably need the maps for something else in the future anyway.

By: ConstantineXVI

ConstantineXVI — Tue, 30 Jun 2009 13:50:24 -0800

PS: Somewhat related to the original question, how accurate is a cellphone (Nokia E71, possibly a N95 as well) GPS chip vs. a standalone handheld GPS from 3-ish years ago (a Magellan, model unknown)?

By: elendil71

elendil71 — Wed, 01 Jul 2009 08:04:36 -0800

A bit late to respond to the last post perhaps, but a recent cell phone GPS app is maybe about as accurate as an inexpensive Garmin etc. Maybe. For what you (or your friend) wants to do with it, any accuracy within 10-15 meters is probably fine. The thing is that sometimes the application or unit in question wont tell you your actual accuracy. You could be within 10 meters, or you could be off by 100 meters depending on satellite coverage etc. The technology is getting better but in general, assume a dedicated GPS unit is going to be better than something bundled into a cell phone.