One of the foremost goals that must be achieved is to model the
average population density throughout the United States. Using
this data, we would like to be able to calculate the risk
- associated with an <em>event</em> taking place somewhere in the
+ associated with an <q>event</q> taking place somewhere in the
United States. This will, in general, be an accident or other
unexpected event that causes some damage to the surrounding
population and environment.
</li>
<li>
- A redundant field, called <em>blkidfp00</em>, which contains the
+ A redundant field, called <q>blkidfp00</q>, which contains the
concatenation of block/state/county/tract. This is our unique
identifier.
</li>
We need to correlate the TIGER/Line geometric information with the
demographic information contained in the Summary File 1 geographic
header records. To do this, we need to rely on the unique
- <em>blkidfp00</em> identifier.
+ <q>blkidfp00</q> identifier.
</p>
<p>
<p>
A Postgres/PostGIS database is required to store our Census
- data. The database name is unimportant (default: <em>census</em>),
+ data. The database name is unimportant (default: <q>census</q>),
but several of the scripts refer to the table names. For
- simplicity, we will call the database <em>census</em> from now on.
+ simplicity, we will call the database <q>census</q> from now on.
</p>
<p>
Once the database has been created, we need to import two PostGIS
tables so that we can support the GIS functionality. These two
- files are <em>lwpostgis.sql</em> and
- <em>spatial_ref_sys.sql</em>. See the <a
+ files are <q>lwpostgis.sql</q> and
+ <q>spatial_ref_sys.sql</q>. See the <a
href="../../makefile">makefile</a> for an example of their import.
</p>
<p>
Since the shapefiles are in a standard format, we can use
pre-existing tools to import the data in to our SQL
- database. PostGIS provides a binary, <em>shp2pgsql</em>, that will
+ database. PostGIS provides a binary, <q>shp2pgsql</q>, that will
parse and convert the shapefiles to SQL.
</p>
<p>
- There is one caveat here: the <em>shp2pgsql</em> program requires
+ There is one caveat here: the <q>shp2pgsql</q> program requires
an SRID as an argument; this SRID is assigned to each record it
imports. We have designated an SRID of 4269, which denotes
<q>NAD83</q>, or the North American Datum (1983). There may be
<h3>Switch from GiST to GIN Indexes</h3>
<p>
- When the TIGER data is imported via <em>shp2pgsql</em>, a <a
+ When the TIGER data is imported via <q>shp2pgsql</q>, a <a
href="http://www.postgresql.org/docs/8.4/static/textsearch-indexes.html">GiST</a>
index is added to the geometry column by means of the
<strong>-I</strong> flag. This improves the performance of the