-------- Original Message --------
Subject: Raster to Vector Alternative
Date: Thu, 20 Feb 2003 10:39:23 -0800
From: "Stefan Freelan" <[log in to unmask]>
To: "Maps and Air Photo Systems Forum"
<[log in to unmask]>,<[log in to unmask]>

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Yes, Raster to Vector (R2V) software exists. Depending upon how clean
your original maps are (how many colors, how many crossing lines
(contours, property, etc) there are, etc.) these can work okay, but its
still a fair amount of work. Especially if you have poor quality maps to
start with. In my limited experience I found that there was a lot of
editing and verification involved. And you still need to get the file(s)
rectified to real world coordinates, so you have the problem of original
maps having poor spatial accuracy...

Another option you might want to think about:

Since most of the roads that you will find on archival maps (at least
for the last couple hundred years) are still in existence, you can start
with an existing GIS (vector) roads layer. Then you use the archival
maps not for spatial location (having to manually digitize or automate a
R2V process, both of which are a lot of work), but only for temporal
presence or absence. In my experience, I found that I only had to
actually create a very few vector features, most already existed in my
GIS. All that was then required was to add temporal attributes
(start-date, stop-date, etc) to the features to create a temporal
database. Overall I've found archival maps to be much better (and easier
to use) for temporal 'location' of features than for spatial location.

Stefan Freelan, GIS Specialist
Department of Environmental Studies
Huxley College, Western Washington University
[log in to unmask]
360-650-2949