Geoscience Reference
In-Depth Information
Once on the TIGER 2000 Geography Network page, select “Preview and
Download” on the left side, and on the next screen, select Colorado via the
map or via the list. On the next screen, select Denver County and press
“Submit Selection.” Do not select any layers yet. On the next screen, under
“Available Data Layers,” select the following five boxes, and then press
“Proceed to Download” at the bottom of the list: Block Groups—2000—make
sure you access block groups and not “Blocks”; Landmark Points; Landmark
Polygons; Line Features—Roads; Census Block Group Demographics (under
“Available Statewide Layers”). Scroll down as needed to find these layers.
Select “Proceed to Download.” Next, you will receive a notice that your data
file is ready. Click Download File to save your data to the folder you created
at the beginning of this activity.
Unzip the file with WinZip, 7-Zip, the extractor that comes with Windows XP/
Vista/7, or other unzipping program. Note that there will be five files that are
zipped underneath this “master level” zip file, plus a readme.html file. Be sure
to Unzip each of the files and extract. When you are finished, you will have
the following files: (1) tgr08000sf1grp.dbf contains the demographic data for
Colorado; (2) tgr08031grp00.dbf, shp, shx contains the block group polygon
boundaries for Denver; (3) tgr08031lkA.dbf, shp, shx contains the geometry
for the roads; (4) tgr08031lpt.dbf, shp, shx contains the Census landmark
points, such as schools and hospitals; (5) tgr08031lpy.dbf, shp, shx contains
the Census landmark polygons; and (6) readme.html contains the metadata
for the Census and GIS data that you will be using. The US Census Bureau
collects data for political areas and statistical areas, and you will use some of
this data for this project. A later chapter will go more into the detail of this
remarkable source of data.
Look at the coordinate system statement on the location from which you
downloaded the data: http://www.esri.com/data/download/census2000_
tigerline/index.html . What is the coordinate system of the data? You will see
that the coordinate system is straight latitude-longitude geographic. In other
words, the data is not in any sort of map projection. Organizations will typi-
cally store spatial data in this way, so that it can be easily read by GIS software
and projected into the map projection of the user's choice.
Start ArcGIS by accessing the software. Then, navigate to the ArcCatalog
application, and navigate to your workspace. Access the metadata tab and
look up the spatial metadata for each layer. Has a map projection/coordinate
system been explicitly defined for these data sets? As you suspected from your
analysis of the map projection in the metadata, no map projection has been
defined for any of these data layers.
You would be fine with working statistically with the data as is, without a
map projection, but since you want to work with it not only statistically but
also spatially, including drawing buffers and other functions that require
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