Several factors may be at play here.
The DeedMapper maps are built from USGS digital data. Any given map when
looked at in isolation has geographic north to the top. But the maps aren't
pure rectangles. They are narrower at the top and wider at the bottom and
the edges are slightly curved, just like the paper topographic maps. This
is because the maps are following longitude lines that narrow toward the
north pole, and they are also representing part of a sphere (the earth) on a
What this means is that when you place multiple paper maps or DM maps side
by side you must rotate them slightly. If you declare one of the maps to be
the starting point then maps to the east of it will be rotated
counterclockwise a tiny bit. The further east you go the more rotation is
needed to fit everything side by side. The same effect works on the west
side except the rotation is clockwise. A series of maps arrayed
horizontally will actually resemble a smile.
Normally you don't notice this effect in platting. It amounts to small
parts of a degree for each map to the east or west of the starting point, so
it would take a bunch of maps to get to 1.5 degrees of error.
When we put our maps together for customers we pick one of the maps to be
the starting point. Actually, the center of that map is the true starting
or reference point. It's the place that all new deeds get dropped, so you
can easily tell where the starting point is for your set of maps.
We don't know what MapMart does with regard to reference points.
, a mapping site we're familiar with, offers custom maps and we
know the ones we've seen are rotated by some amount, several degrees in some
cases. The amount of rotation apparently depends on the longitude of the
particular map being looked at. Perhaps the site you're using is similarly
structured? If you look at an intersection point where topo maps come
together you can see with your eye whether the map edges are running true
north-south (up/down) and east-west (left/right).
----- Original Message -----
Sent: Saturday, November 12, 2005 10:26 AM
Subject: [DMU] Deed Mapper Maps Projection and Datum
I recently purchased a custom-sized digital raster graphic (DRG) file
are scanned images of USGS 1:24000 quad maps) from MapMart.com
about four quads in Shenandoah County, Virginia. I used MapMart's
projection (UTM) and Datum (1927) settings. I cannot get this DRG to
placement I made on the Deed Mapper maps and was wondering if there is a
difference between the UTM/Datum for the DRG and Deed Mapper maps.
My Deed Mapper files contains about 17 surveys that are spread along a
north-northeast line of approximately ten miles. When I use the DRG as a
instead of the Deep Mapper maps I used to place the surveys, I get a
counterclockwise rotation of the DRG of about 1.5 degrees. I have a
placement of the most southwesterly survey (county border & prominent
line), so the maximum rotation problem appears in the most northeasterly
It is not just my surveys that do not line up, it is the roads as well
place a bogus survey at a road intersection on the Deed Mapper map, that
survey does not match the same road intersection on the DRG. I have
rotate the DRG graphic using Adobe Photoshop Elements; however, although
get it closer, it still does not match. I am guessing that I cannot get
to match because the center of the rotation problem is not the same as
center of the graphic.
Does anyone know the projection and datum used on the Deed Mapper maps.
Also, has anyone had similar problems and found a way to resolve them?
Thanks, Michael Cummings
==== DEED-MAPPER-USERS Mailing List ====
Send all messages and replies to <DEED-MAPPER-USERS-L(a)rootsweb.com>.
Search Family and Local Histories for stories about your family and the
areas they lived. Over 85 million names added in the last 12 months.
Learn more: http://www.ancestry.com/s13966/rd.ashx