Geography Reference
In-Depth Information
What is interesting about the comparison of the sizes of these two rasters is that, while the 5-meter
resolution raster contains four times as many cells as the 10-meter resolution one, the dataset is not four
times as large (which would be 300 percent larger). In fact, it is only about 100 percent larger. So,
it is not the case that doubling the resolution quadruples the compressed dataset size—far from it!
This happy occurrence is the result of the data compression techniques discussed in Chapter 4, which
take advantage of the fact that, with smaller cell sizes the cell next door to a given cell likely has the
same value.
16.
Restore ArcMap (The title should still be Preserve_Environments.mxd) and remove Soils_
rr10m_X and Soils_rr5m_X from the map, since they have illustrated their point. Since none of
these datasets we have been working with is very big, and they didn't take very long to create,
let's increase the resolution—say, to 2 meters. Make Soils_rr2m, being careful to put it inside
the mdb geodatabase.
17.
Add the feature class Landuse
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from
___IGIS-Arc_
YourInitials
\Spatial_Analyst_Data
\WC_Boat_SA\Wildcat_Boat_SA.mdb\Area_Features)
to the map. Using 2-meter resolution, make a raster dataset of Landuse, called Landuse_rr2m
inside the geodatabase. Use LU-CODE as the field to make the “value variable” of the raster.
Zoom to the extent of Landuse_rr2m. Turn off all layers except the Landuse pair. Zoom to the
extent of the Landuse Layer. Make the Landuse Symbol No Color or Hollow. By zooming in, look
at how closely the cells approximate the Landuse boundaries.
18.
In ArcMap open the attribute table of Landuse_rr2m. How many cells of value 100 are there?
________. How many square meters does each cell represent? ________. So, how much area,
in square meters, is occupied by the land use with LU_CODE equal to 100? ________.
19.
Just as a check, open the attribute table of the feature class Landuse. Click Table
Options. Using Select By Attributes, select those records with LU_CODE
100. Show only
selected records. Run statistics on Shape_Area. What is the sum to the nearest square
meter? ________. Compare this number with the area you calculated in the previous step.
Feel encouraged by the reasonably close agreement between the two areas. Clear the selected
features and records.
=
The results of the calculations regarding area should be confirming, even though they are not
exactly equal. To say it for the umpteenth time: All GIS representation, whether vector or raster, is an
approximation of reality.
20.
Save the map as WC_Boat_Area_Map.mxd in WC_Boat_SA. Dismiss ArcMap.
Next, you will convert (create rasters for) the feature classes Roads, Streams, and Sewers. To do this
properly, we should first verify the Environment variables, so that we can be sure the extents of all the
datasets will be the same.
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We called this dataset Landcover when we worked with these datasets before. The terms land use and land cover are
technically not the same, but are often used interchangeably.
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