Impact of Climate Change and Land Use on the Southwestern United States

Information resources

This page is a discussion of
Population Density Data by County: An Interactive Database


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A comment by Henk Meij

Compliments on the very nice layout of this population
information resource. Some general questions I have are:

- can a page be added describing what software components are
used to handle map display, graph/plots, and information
retrival?

- what is the reason for the lack of the 1990 data point?  1993
is an estimate (?) and if so, should be flagged as such.

- How are new/old and changing boudarry conditions handled,
what are the boundary data sources?

Finally, it is ofcourse fairly misleading to look at 
population density at the county level, the latter not being 
very homogeneous in composition at all.  Densely populated
counties may have extremely remote, isolated areas and vice
versa. The primary source of increases in pop density in the
west is in migration. The graph would be extremely useful
if it showed the rate of in-migration at each time interval
showing it's tremendous contribution to population increases
of each county.

-Henk
SEDAC Project Scientist

Explanation and some details

A comment by Peter N. Schweitzer

I got the data from Martin Chourre and Stewart Wright,
who describe them in good detail in their paper for
this conference.  Martin has indicated to me that the
data I call "1993" is in reality 1990 census data plotted
on more recent (1993) county boundaries.  So the program
should refer to the latest data as 1990 rather than 1993.
We (the workshop administrators) decided that we shouldn't
fix things like this in "mid-stream" because the fixes
will make the comments confusing.

I agree that county-level population data aren't good
for understanding all of the processes that affect
local population density for the reasons you mention.
This is intended as a broad summary only.  I suspect,
however, that it would be a lot harder to depict the
data at a finer spatial scale because census tracts 
have likely changed considerably in the last 100 years,
so it might not be possible to create a credible time-
series for smaller geographic units.  Just guessing.

Anyway, the boundaries change with every decade (see
the discussion by Chourre and Stewart on this).  Some
counties are split in two or otherwise change their
total areas.  Where the area changes I've got the CGI
outputting the area as a column in the table, but if
the area didn't change, I leave that column out.  The
plots don't show (or correct for) changes in area, so
some plots of total population have dips that can be
attributed to loss of area.

The data are stored in a database on the server using
mSQL (mSQL is used for the conference's users, documents,
and document threading as well).  The county boundaries
from the Chourre and Stewart data were converted to
imagemap areas by my intern Yew Yuan using Arc/Info's
ungenerate command followed by some C programming.
When you click on a county, the CGI program (written
by me in C) gets the county's data from the SQL database
and creates the plot image if the plot image has not
already been created (since they don't change, it makes
sense to save them rather than generate them each time).
Then the data are expressed numerically in a table and
the plot file is included inline (<img src="...">).
The plots are created as GIF images using Boutell's
gifDraw library, a set of rudimentary graphics routines
callable from C that create reasonable (if primitive)
GIF images.  So aside from the first page, all of the
rest are generated through the CGI.  Most of the code
is fairly specific to our system here, but if you're
really interested, I'd be happy to show it.

Please let me know if I can provide additional information
or assistance.

USGS

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