Geography Reference
In-Depth Information
FIGURE 2-33
tool is not being used, you will see the elevation of the DEM post when you pause over a
given geographic location. See Figure 2-33. Using Measure and MapTips, find the steepest
average slope you can—where the land drops __________ feet in elevation over a distance
of ________ feet.
45.
Examine the COLE_DEM entry in the T/C, after widening the pane enough to see all the text.
Collapse the COLE_DEM entry, to hide all the values and their symbols. Open the attribute table
for COLE_DEM. It is called a value attribute table; it has an extension of “vat”. The number of
different heights that are represented is 529. The Value field contains the height of the grid
“post” in feet. The Count field indicates how many posts there are of that height. How many
posts are there of height 1000? _________.
46.
Since this table is more vertical than horizontal, let's dock it on the right-hand side of the
screen and resize it so that we can just see all three columns. Select the records whose
elevation lies between 901 and 1000, by clicking the box to the left of the record with
elevation 901, scrolling with the scroll bar to 1000 (being careful not to click on any other
boxes), and then holding the shift key down and clicking the record that shows elevation 1000.
(Alternatively, you can click to select 901 and drag your mouse to 1000. You may find this to be
somewhat difficult because the table can scroll very quickly. So, if this doesn't work very well
because the table scrolls by too quickly, do it in stages, using the vertical scroll bar to scroll the
list; hold down the Ctrl key while clicking to select each successive set of records.) Once those
100 records are selected, run statistics on the Count attribute. Recall that you will get results
based on the selected records only. Use the Selection Statistics of cole_dem.vat window
to determine how many posts (the Sum) there are with elevations between 901 and
1000. __________. How much surface area in acres would that be? __________ acres.
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