Open a blank Arc map and add the New Castle County road, rail,
stream and water polygon shapefiles (or access your previous
map and remove the Census tract, block group,
block and school district layers). Specify a
DE State Plane (NAD83, meters) coordinate system for the data
frame.
Load the
the Spatial Analyst and 3D Analyst
extensions (Tools-Extensions, check the boxes; then right mouse-click
on "Tools" in the menu bar to access the toolbars). From
the Spatial Analysis Lab website
www.udel.edu/FREC/spatlab/dems/county
download the raster file
New Castle DEM (DE
State Plane NAD83), unzip it and use
the ArcToolbox "Conversion--To Raster--ASCII to Raster"
conversion tool to
import it as a raster layer into a blank map. This is a
30-meter resolution digital elevation model (DEM) of New Castle County,
interpolated from patched hypsography files for 7.5-minute quads (USGS
1992-93), in
DE State Plane, NAD
1983 (meters) projection--set your Data Frame to this
projection. Note that while the X-Y units are meters, the elevation
(Z) values are in
feet (1 foot = 0.3048 meters).
If you haven't already done so, use Data--Export Data to create a
copy of your county boundary file
in the coordinate system of the
Data Frame (DE State Plane).
Before starting any raster analysis, you should always specify
the Spatial Analyst Options that will determine the coordinate system,
extent and cell resolution of the raster maps you create.
In the Spatial Analyst Options "General" tab, specify
a
working directory on your data stick. The analysis Coordinate System
should be the same as the active data frame. If you wish,
you can specify the DE State Plane
version of the county boundary shapefile as
a mask;
any subsequent raster maps you create will fill the county
boundary polygon only.
In the "Extent" tab, set the Extent the same as the
DE State Plane
county boundary shapefile; you should see State Plane bounding coordinates
(in thousands),
not lat-lon coordinates.
In the "Cell Size" tab set the cell size the same as
the DEM (30);
you should see calculated row and column counts for this map extent.
Any raster maps you
create from here on will conform to these settings.
If you do not set these Spatial Analyst Options correctly, your
subsequent analyses will be based on some arbitrarily large cell resolution
and your results will be inaccurate or entirely wrong.
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Save a series of small (no more than 4"x8")
GIF
images of
each of the following:
- the DEM displayed with an appropriate
stretched color scheme,
with the line
and polygon water features overlaid in dark blue.
- a hillshade raster map derived from this DEM, with
the "Model Shadows" box checked. To increase its contrast,
specify a "histogram equalize" Stretch type
in the Symbology settings.
Drag the hillshade raster under the DEM in the legend.
Display the DEM with 50% transparency on top of the hillshade.
Once you get a really good-looking DEM with hillshading showing through,
you can
group the DEM and hillshade rasters and save them as a group
layer file.
- a slope raster map derived from the DEM using a Z-factor of
0.3048 to convert elevation values from feet to meters.,
Use an appropriate color scheme for the
following 8 slope
categories: 0-0.5, 0.5-1, 1-2, 2-3, 3-5, 5-10, 10-15 and 15-99 degrees.
Overlay the water features.
- an aspect map derived from the
DEM; the default color scheme is ok.
- a 25-meter-interval elevation contour shapefile
derived from the DEM; colorize these
by their CONTOUR values.
Note that, by default, some raster modules including the
Raster Calculator will create new files in
temporary workspaces that will not be saved with the rest of your
project. If you want to keep permanent copies of these, make sure
your workspace is specified in the Spatial Analyst Options menu,
and use the "Make Permanent" option on raster layers generated by Raster
Calculator.
B. Habitat Analysis:
Suppose you are hired to identify prime habitat areas for the
endangered pickled strumpet (Trollopensis
bibulosa) in New Castle County. Field biologists have
given you the following habitat criteria:
- slope of 2 degrees or less, and
- either freshwater wetland, i.e., wetland with
elevation >5
meters (or 16 feet)
or forest within 250 meters of streams,
and
- at least 200 meters from primary roads (A1x's,
A2x's, A3x's and A63's in
CFCC field) and
at least 100 meters from all other roads and at least
100 meters from all rail lines.
Add the following layers to your map:
- 2007 land-use/land cover shapefile
(codes in LULC1 field: 1=developed; 2=ag; 3=brush; 4=forest; 5=water;
6=wetland; 7=barren)
- the TIGER roads, rails and streams shapefiles you used
in the previous project.
- keep the DEM you used above.
- keep the slope map you derived from the DEM
Use Spatial Analyst tools such as Raster Calculator,
Distance, Reclassify, Neighborhood Statistics, Convert, etc. to
create a map of each criterion, and then derive a map of landscape
clumps in the county that satisfy
all
of the pickled strumpet's habitat requirements. You will finish this
part of the analysis with a logic calculation that combines all these
criteria and yields a raster map of suitable habitat clumps (1's) on a
background of zeroes.
Some suggestions/comments:
- Take some time to explore Arc's raster and vector
capabilities. There are lots of alternative strategies for doing
this analysis, so if you get stuck on one strategy, try another!
- You can use Arc's Analysis
Tools--Proximity--Buffer tool to create a shapefile of
buffer polygons around road, rail and water
features, but this can be slow.
It's much easier to run Spatial Analyst's Distance
module (with no maximum distance specified) on them and the use the Raster
Calculator to extract
appropriate raster buffers from the funky-looking Distance map.
But remember that the TIGER shapefiles are actually unprojected lat-lon
data, and merely displayed in DE State Plane coordinate system.
If the Distance tools don't work reliably on an
unprojected (lat-lon)
shapefile, right-click it and use Data--Export Data to
create copies of
your road, rail and water shapefiles in DE State Plane
coordinates (the data frame's coordinate system);
alternately you can use the Projections utilities in
Arc Toolbox.
- When creating a Distance map, you should generally NOT specify maximum distances,
since you will get useless
NoData cells outside the specified maximum distance.
- If you select certain features in a shapefile or
categories in a raster (e.g., just the major highways in
a roads shapefile,
or just the wetland clumps in a land-use raster),
Spatial Analyst's Distance tools will calculate distances
to the selected features or categories only.
- If you select certain shapefile features or raster
categories, Spatial Analyst's Convert tools
(Features-to-Raster or Raster to Features) will
convert only those selected features.
Be careful when converting selected shapefile features to
raster: the resulting raster will have a
background of "NoData" values.
"NoData" is not the same as zero; you can't do anything with
NoData values!
I recommend rasterizing the entire land-use map using the LULC1 field
(first digit of the land-use/land cover code),
then extracting the forest and wetland clumps as
needed.
- Pay attention to the execution speeds of raster-vector
conversions,
buffering, etc....if some task takes a long time to execute, see if you
can simplify the task or try another approach. For example, since
you're only studying forest and wetland areas, you don't need to buffer
road or rail features that aren't within those areas.
Once
you have all the suitable habitat clumps, you will see that most of
these clumps are small and fragmented. Since the pickled
strumpet is very sensitive to disturbance at the edges of its habitat,
conservation efforts should focus on the habitat clumps with the
largest area and highest compactness (area divided by perimeter
squared).
Extract the habitat
core areas--cells that are more
than 60 meters (2 raster cells) inside the nearest clump edge.
You can use Spatial Analyst's Neighborhood Statistics (sum
within a 5x5 neighborhood: cells with a neighborhood sum of 25 would be
"core" habitat).
Select the "25" category from the attribute table
of the neighborhood sum map, and
convert these core clumps to shapefile polygon features.
Open the core polygon attribute table and create double-precision
(not integer!) "Area," "Perimeter"
and "Compactness" fields.
Right-click the "Area" field header and use "Calculate Geometry" to
calculate polygon areas (in square meters).
Right-click the "Perimeter" header and calculate perimeters (in meters).
Then calculate a compactness index.
If you multiply area times
12.56637 (=4pi) and divide by perimeter
squared your compactness index will range from near zero
(approximating a true fractal)
to one (a perfect circle).
Select the 10 or 12 "best" (e.g., biggest, and favoring more compact)
core features and display these in a distinctive color. You should see one
cluster of biggest cores something like the red features here.
Use Spatial Analyst's Zonal Statistics module to analyze
the elevation mean, standard deviation, etc.
of each of these biggest core polygons. A program bug makes
the chart worthless; you want the table.
Join the statistics table to the core polygon
shapefile (you will need to examine the tables to see
which fields to match on).
Label each of the major core polygons with its mean elevation.
Now that you know where the main cluster of prime habitat areas are
located in the county, download the 1997 digital
orthophotos for this area (JPEG format) from the clickable
map. (Don't confuse the southwest corner of New Castle County with the
southwest corner of Delaware!) To use these in ArcMap, you
will also need the corresponding
header (georeferencing) files for each airphoto. These
orthophotos each cover one quarter of a 7.5-minute quadrangle, e.g.
"clayton_ne.jpg" and its header file "clayton_ne.jgw" cover the
northeast quarter of the Clayton quadrangle.
Make sure you save the JPEG images and JGW header files
to the same directory. Save the JGW files as "All Files"
rather than ".TXT" so they retain
the ".jgw" filename extension.
(I strongly recommend that you use Mozilla Firefox;
MS Explorer's default modes will mess up both the images
and the header filename extensions.)
When you add the orthophotos to your map, they
should tile nicely under the shapefiles.
Superimpose the prime habitat areas and whatever other
features you want on the tiled orthophotos. Notice that the
positional accuracy of the TIGER features is not as good as the orthophotos.
Write up a brief consultant's report outlining your procedures,
and describing the particular areas you recommend for protection.
Do a little research into land protection programs: what
programs are out there that would be likely to support this
protection effort? What protection strategies would you
recommend? How much would these strategies cost to implement?
C. Raster 3D Viewing:
Zoom your map to the piedmont area of the county.
In the Spatial Analyst Options reset the Extent to "Same as
Display." Check the cellsize is still 30 meters.
Use the Raster Calculator to create a copy of the DEM with this
smaller extent.
Use ArcScene (icon in 3D toolbar) to create a visually-appealing 3D
oblique-angle view of the piedmont DEM.
Set the Base Heighs from the DEM itself, multiplied by some Z-factor
to make the terrain look more dramatic. (Since the DEM's Z-values
are in
actually feet rather than meters, the elevations are already
exaggerated three-fold before you start increasing the nominal
Z-factor!)
Check the hill-shading option in the Display tab.
Overlay roads, rails, streams and/or water polygons (these shapefiles
should be in the same coordinate system as the DEM) using
the same base height settings.
Maybe try draping
the land-use layer or some orthophotos semi-transparently over the DEM--
make some sweet eye-candy!
If you're really ambitious, try
making a brief flyover video clip, using
Arc's movie-capture utility
to capture some panning and zooming, etc.
"You know, I have one simple request, and that is to have
sharks with frickin' laser beams attached to their heads.
...Throw me a bone here! What do we have?"
...
"They're mutated sea bass."
"Are they ill-tempered?"
"Absolutely."