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diff --git a/www/faq.html b/www/faq.html index d974fc78..139f3139 100644 --- a/www/faq.html +++ b/www/faq.html @@ -493,9 +493,12 @@ works.</p> <p>If you're using <tt>gpsd</tt> with software that plots your position on a map, and you seem to be getting latitude/longitude that is at a fixed offset from reality, it is possible the base datum of -the map is something other than the WGS84 GPS uses. An important case -of this is North American Geodetic Survey maps based on NAD27; you may -see a displacement of as much as 100-150m with respect to WGS84.</p> +the map is something other than the WGS84 GPS uses. A +frequently-occuring case of this is older maps in the United States +based on NAD27 (e.g., USGS topo maps); you may see a displacement of +as much as 100-150m with respect to WGS84. While modern datums (e.g., +NAD83) are almost all very close to WGS84, typically each area of +world has an older datum that only agrees at the 100m level.</p> <h1 id='sleep'>Why does my GPS get lost when I sleep/wake my laptop?</h1> |