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SIY5.TXT Topographic Maps and Aerial Photographs 35
Chapter 5
Topographic Maps and Aerial Photographs
The first survey which you should do on any piece of land is to
simply to look at the topographic map. Topo maps at a scale of
2000 feet per inch are available for most of the United States
for less than five bux [$5] delivered.
See USGS or Timely Discount Topos in Chapter 14 for instructions
on where to order a topo map in the USA.
In other parts of the world, write the Geological Survey in your
capital.
Having taught topo map reading at the University of Kentucky, I
know that I cannot teach you to read a topo map by mail. The
only way for you to learn to read topo maps is to compare a topo
map and the real ground. Order the topo map for a familiar area,
like around your home. Be sure that you get the pamphlet
"Topographic Map Symbols" too. Then walk around with the map,
compass, and symbol sheet. Orient the map so that the North
Arrow points the same way as the compass needle. Compare the map
with reality.
The only really different feature of the topo map is the
topographic contour lines, those random brown squiggles doodled
all over the map. If these contour lines still seem like random
brown squiggles to you, try this.
Imagine the Second Great Flood. As The Sea rises, the new
shoreline will move up into the land. At any given rise in The
Sea level above today's Mean Sea Level (MSL), the new shoreline
will be represented by the contour line at that level. You can
see [hopefully] that in level land, a large area will be flooded
by a small rise in The Sea. On steep ground, the new land
flooded would be only a narrow strip. Bays will reach up into
the valleys, and ridges will extend out into The Sea. High
ground will eventually become a chain of islands.
The contour lines do all these things, without the necessity of
all that water.
SIY5.TXT Topographic Maps and Aerial Photographs 36
Be sure to ask for the free pamphlet "Topographic Map Symbols"
when you order your first topos. Every house, barn, creek,
river, rapids, dam, highway, road, jeep trail, government
boundary, school, cemetery, church, pond, lake, picnic grounds,
railroad, high tension line, pipeline, mine, strip mine, wood
lot, swamp, spring, windmill, &c, etc, et cetera is marked with a
special symbol. In Township and Range country, the section
corners and lines are marked. Sometimes fence lines are on the
map too.
Once you have learned to read a topo map on familiar ground, you
can read a map of any place of interest. Map Reference Libraries
are located at most college Geology and Geography Departments,
and at major city libraries. The addresses of these Map
Reference Libraries are listed on the Index Map for that state.
Many public libraries have topographic maps of the local area.
Topos are so quick and cheap from Timely Discount Topos that you
can order them for an area of interest and then use them for
impressive wallpaper.
Each state has an index map or a "green book" which you can use
to determine the proper map to order.
Each topo covers about 7 miles across for the standard 7.5 minute
map. It is named for some prominent feature, generally the
largest city, village, or hamlet, but sometimes for some other
landmark. Each map tells which maps join on the sides and
corners. You can make three guesses of the proper map and get
the index map or "green book" and a "Topographic Map Symbols"
pamphlet all for less than ten bux [$10] delivered. This will
make you an instant expert on local land use.
Aerial photographs for agricultural areas are available in your
county ASCS office. See Chapter 14. Visit them with the area of
interest marked on your topo map. Use the office photo mosaic
index to locate the aerial photo covering your land. It may help
if you know the name of a nearby farmer so that the clerk can
look up the photo of his farm.
SIY5.TXT Topographic Maps and Aerial Photographs 37
County ASCS offices usually have photos of all agricultural land
at a scale of 660 or 1000 feet per inch. Fields, trees,
buildings, roads, cow paths, streams, fences, etc., etc. can be
easily seen on the photos. ASCS may have their version of the
property boundaries and ownership marked on the photos. Where
the property boundaries are field boundaries, the ASCS version is
usually quite accurate. In woodland, they are guaranteed
incorrect.
You may also be interested in using a stereoscope. With this
instrument, two aerial photos are combined to create a 3-D image
of the land. This is one of those things which you just must see
to believe!
A good pocket stereoscope with glass lenses for reading aerial
photos is $24. A worthless model with plastic lenses is $4.
In non agricultural areas, the BLM, National Forest, Corpse
[sick] of Engineers, or other agency may have aerial
photography. Sometimes in color. I doubt that there is any part
of the United States for which aerial photography is not
available.
I can't teach you to read topo maps or aerial photos by mail.
But if you have trouble finding the proper item, I might be able
to help. And if you have any interesting scientific or
engineering applications, I'd be glad to consult. Agriculture,
geology, hydrology, botany, forestry, wildlife management,
archaeology, land use planning, flood management, historical
research, construction engineering, and law enforcement come
quickly to mind.
The Silva Ranger is especially handy for determining your
location on a topo map. First, find some recognizable landmark
both on the ground and on the map. Then measure the direction to
it with the Ranger. Next, place the Ranger on the map with the
edge passing thru your landmark and the meridian lines inside of
the compass dial aligned with the north-south lines on your topo
map. Your location is along this line. If you shoot and plot
the direction to another landmark, your location will be where
the two plotted lines cross. You can get a feel for the amount
of error involved by plotting directions from several landmarks.
With the Ranger this is so fast and easy that it can be easier
done than said, once you find your landmark. If you have ever
tried this with a Brunton pocket transit, protractor, ruler, and
pencil, then you will really appreciate having everything in one
instrument and the protractor already set to the proper reading
too. Geologists' Heaven!