Geography Reference
In-Depth Information
What is that designation? _____________________________.
The way ArcGIS copes with the immense size of LiDAR datasets is by showing only a reasonable amount
of information, based on the scale of the display. In what follows, you will experiment with viewing the
terrain layer with various levels of scale.
18.
Highlight the contents of the scale text box in the Standard toolbar, type 5000, and press Enter,
which changes the scale to 1:5000—or rather will change the scale to 1:5000 after a bit of
time, depending on the speed of your computer; a lot of computation is taking place. If you now
look at about the middle of the terrain layer, you will see the water treatment plant, which you
did not see before because of the smaller scale.
19.
Look at the T/C. Notice that, where before it said *Overview Terrain, it now gives a Z Tolerance
of 4. This value basically indicates that only those elevations that are different by 4 feet are
represented in the image.
So, this is the mechanism that ArcGIS uses to cope with the massive amount of data: When a
relatively large area is shown the level of detail is reduced. As the scale gets larger, more detail
is shown, but the amount of computation needed does not greatly increase because the area
shown is smaller.
20.
Change the scale to 1:3500. Pan the image so that the water plant view is in about the center.
What is the Z Tolerance now? ___________.
21.
Record the Z Tolerance for the scale 1:2500 and examine the map. _____________Then
1:1500, still keeping the water plant near the center by panning. _______________. Finally
use 1:500. The Z Tolerance has become zero, indicating that every data point is being used to
generate the TIN, regardless of difference in elevation. Dismiss ArcMap without saving changes.
Exercise 2-6 (Project)
Geodatasets of Soils, Rocks, and Land Cover
The type of soil that exists at a location is important for agriculture, for assessing the effects of erosion,
and for other reasons. The rock below the soil is of great interest to those who investigate the resources
of the planet. In the database Kentucky_River_Area_Data.mdb, we have a Personal Geodatabase Feature
Dataset called Quadrangle_Data, which contains feature classes cole_soil_polygon and cole_rock_polygon.
In the soils data, the different classifications appear in a field named MINOR1 of its relational database
table. The different classifications of surficial rock types are identified in the NAME field of its table.
The origin of these databases is not given, nor the meaning of the classifications. While these are real
datasets, they are not valid for display or analysis, other than in a tutorial sense.
1.
Display a soils personal geodatabase feature class
: Work with River_Map_5 in ArcMap. In [___]
IGIS-Arc\River, find the MDB (Microsoft Access Database) file named Kentucky_River_Area_
Data. Pounce. Find the Feature Dataset Quadrangle_Data. Double-click. Add cole_soil_polygon
to the map. Drag its title to the bottom of the T/C. Make sure all image layers, the DEM, and
the TIN above it are off. Turn everything else off as well except the GPS and Vectors group.
Zoom to the extent of cole_soil_polygon. You will note two blank areas—one to the southwest
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