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    Reading topo maps
    From: Bill B
    Date: 2006 Oct 31, 20:42 -0400

    When trying to determine Alex's elevation from my topo map, I found it a bit
    confusing.  The major contour lines are at 50 ft elevation intervals.  If I
    recall those are always 5 units apart, so minor lines are at 10 ft
    intervals.
    
    When one gets near the river valley, with a drop of 200+ ft in a quarter
    mile on the West Lafayette side, they are packed together, often less than a
    millimeter apart.  Once out of the valley, the 700 ft line can meander along
    for 4 or 5 miles (radius), with small 700 ft shapes within.  The problem
    then becomes determining whether the minor lines between the 700 ft lines
    indicate a rise or fall.  It is not as easy as determining what is happening
    as when the "circles" are more or less concentric like isobars, or seeing
    valleys, ridges, or saddles.
    
    In some cases minor lines that extend for many miles will be labeled once
    (690, 680, 680, etc.)  Problem being that one tag on a line with 10-20 inch
    length that passes through residential and commercial areas, roads and
    highways etc. and converge with other minor lines so it is almost impossible
    to track one to the area of interest.
    
    There are very few small areas marked with the depression cross lines.  Any
    tricks or tips, other than the old mach-one eyeball on site on how to
    interpret what is happening?
    
    Thanks
    
    Bill
    
    
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