Article: 139574 of sci.geo.satellite-nav From: Jack Yeazel Newsgroups: sci.geo.satellite-nav Subject: Re: "Tiger" Maps and Garmin GPSes. Date: Sat, 08 Apr 2000 14:42:38 -0400 Organization: Un-organized Lines: 24 Message-ID: <38EF7D9E.7D554D34@FinalApproach.net> References: <8cgsr0$ms6$3@nw001t.infi.net> NNTP-Posting-Host: d1.56.4f.ed Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Server-Date: 8 Apr 2000 17:42:35 GMT X-Mailer: Mozilla 4.05 [en] (Win95; U) To: John Galvin Path: news1.meer.net!news3.best.com!news2.best.com!feed1.news.rcn.net!rcn!cpk-news-hub1.bbnplanet.com!news.gtei.net!firehose.mindspring.com!not-for-mail Xref: news1.meer.net sci.geo.satellite-nav:139574 John Galvin wrote: > > A little clarification here. Garmin's R&R are based on the Tiger data from > the Census bureau. The Tiger data itself, is derived (poorly) from the USGS > 100k DLG (vector) data. That data is derived from the USGS 100k DRGs > (raster data). The 100k DRGs are based upon generally, old field survey > data, updated with data derived from USGS DOQs (aerial photography). > > The Garmin Topo maps are derived from the USGS 100k DLGs (and DEMs). This > derivation path bypasses the Tiger data entirely. That results in much > higher quality, even if it means that it's not as uptodate. The Tiger data > is updated every couple of years (93, 95, 97, 98). The 100k DLGs, maybe > every 5 to 10 years. Thanks very much for that explanation... My experiments have confirmed what you say... What is your understanding as to where the ETAK database comes from -since the USA Topo maps seem to be almost as accurate??? (See: http://Jack.FinalApproach.net/mapcomp.htm ) -- Jack Get general GPS information at http://joe.mehaffey.com/