[meteorite-list] Online Geological /Geophysical /Topological Map resources

From: Mr EMan <mstreman53_at_meteoritecentral.com>
Date: Thu, 4 Oct 2007 02:05:05 -0700 (PDT)
Message-ID: <814848.42587.qm_at_web51012.mail.re2.yahoo.com>

Having received some request for more online map
information, here are some tips for locating free on
line maps.(Primarily USA). The good news is that
there is a federal program to publish digital products
online that will provide complete national coverage.
The bad news is that it is a federal program...
subject to manpower and funding constraints but it is
a very good start. The Internet is a source for many
maps of other countries. I have viewed geological maps
of Oman and even the Moon and Mars online.

Geological and Geophysical Maps:
Finding The Map you need:
Traditionally, one went to a state bookstore to
purchased a paper map hoping it was still in print.
The trend today is to publish them online with free
access. Tennessee will no longer be printing maps in
advance. Maps that aren?t online can be purchased for
$20 a map, printed straight from a digital file.

The quick and easy solution for links to state
geological maps is About.com
<http://geology.about.com/> AND/OR
<http://geology.about.com/library/bl/blcontent_a-z.htm?terms=about+geology>

About.com pre-searches and assembles all types of
classes of information. If you go to their Geology or
Maps sections and poke around there are pages for
State Geological Maps AND State Geological
Organizations. (There is also <geology.com> with
similar sources.) They also list state authorities
and link to their websites. Once in those you may
frequently find a free downloadable map for the local
area you are looking for. The USGS , as mentioned
above has taken great steps to centralize the search
for geological maps.

State and regional authorities aren't uniformly named.
In many states they are under DNR(Dept. of Nat'l.
Resources) some are under State Mining authorities,
some are simply quasi-public such as Geological
Society(e.g. Alabama). About.com lists them all. You
can also Google for maps but it can be trial and error
to structure your inquiry given the lack of
standardization.

The US Geological Survey has a master database of maps
both online and paper at this portal:
<http://ngmdb.usgs.gov/> --unfortunately it has a
convoluted search system, having recently merged other
catalogs. Of note: Kentucky is one of the only states
that has placed it's entire geological map quads set
online.

Back Doors:
Owing to forward thinking, many states and federal
agencies have designated certain public and university
libraries as repositories for map products even for
far away places. Some of those libraries have scanned
paper maps into their online collections even where
states have not. These are usually in Adobe Acrobat
Format as they weren?t generated digitally. Some maps
generated for say an environmental project or mining
district will include bedrock geological information.
I searched for years for any copy of an out of print
Pennsylvania map only to find it in online in a
California University system. So if you don?t find it
initially get creative in your searches.

What Maps there maybe:
Quads (short for Quadrangles: the basic map sheet
format) are "indexed", usually on a state map which
graphically shows the name and position of all the
quad map sheets in that state. Some indexes will just
show the name of the map sheet. In that case you can
always fall back on the Federal "Index of Topo
(topological)" maps to locate the name of the sheet
you are looking for. Geological quads follow the name
of the topo quads, which in turn are named after a
town, community, or feature fond on that sheet. The
sheet will be named at the top and have the names of
the eight adjacent sheets around the edges. Quads come
in different scales aka sizes-- the basic size is
called the 7.5 minute Quad because it spans 7.5
minutes of latitude and 7.5 minutes of longitude(high
latitudes of course cover more than 7.5 minutes owing
to convergence of longitude towards the poles).

I won?t cover map reading here because there are
several online lessons on how to read topological and
geological maps. In the interest of brevity I suggest
one google "How to read a topo/geological/map etc."

Quads also come in larger formats which may include
several portions of states. For example the Knoxville,
TN Quad covers parts of 10 states. This brings up
regional/ special geological maps(e.g. The Grand
Canyon, New Madrid Seismic Zone, etc.) These may cover
parts of several quads. Geological quads may be
published in bedrock or surfacial versions in
glaciated areas where one needs to distinguish between
ancient and tertiary-aged deposits.

Printed quads falling along political boundaries are
occasionally truncated to the parts within the state
publishing the map, however, the digital quads usually
will include the full map data from adjacent parts
which overlap state lines. Sometimes you can get
geological data by reverse searching adjacent state
quad indexes to find published data when the home
state hasn't published their maps online.

Digital maps follow formats which are derived from
standard data systems (e.g.GIS,GMLJP2,GML, GPX etc.)
which tends to produce huge files too large for many
home systems to display, but don?t dispair. There is
a free program called "ExpressView" (formerly Mr SID
Browser Plug-In) which makes the maps available in
great detail on home computers which won?t max out
memory. LizardTech is the publisher and the map
reader is free to download and use. There are a mix of
plug-ins and standalone applications for WIN and Mac
OSX
<http://www.lizardtech.com/download/dl_download.php?detail=geo_expressview_plugin&platform=win>
 Two other resources of mention are Google Earth and a
software program called TerraBrowser.

When you need something more or on the road:
Sometimes the geological map is just a black and white
miniture overlay (e.g. Pennsylvania DNR Map6).
Sometimes you are looking for a dig site,a reported
meteorite fall or, one wants to hook it to a
GPS/Laptop. A topo is what may be the only thing
available. One can find most topo maps at the above
state and federal sources. One can also purchase
state and national digital map sets that have
different complete of detail. I use Topo USA and
National Geographic ?BackRoads Explorer? to supplement
the online resources. I also have a modem compatible
cell phone when I find myself on a road trip and
happen upon a geological curiosity.

This post is a far from exhaustive list of resources
but a good place to start. Fortunately, the internet
is one giant map room.

Elton
Received on Thu 04 Oct 2007 05:05:05 AM PDT