Saturday, January 7, 2012

Making maps in New York - hydrography

We left off last time with a map that has the street grid (well, sort of, it still needs to be styled!) and the contour lines (so that if I'm looking at a street or trail, I can tell how steep it is).

The next key piece of information that I need for a walking map is whether I'll get my feet wet: where is the water on the surface? So, let's look at some data sources for hydrography.

The hydrologic features are, we already saw, in the digital raster quadrangles, but (I repeat yet again) we don't want to use them, because they don't scale, and because they're cut off at the margins. So let's get vector data instead.

Fortunately, for New York, surface water features are "one-stop shopping." New York State's Office of Cybersecurity has two shapefiles, one with line features and one with area features, that cover the entire state and are suitable for rendering at 1:24000.

After downloading and unpacking them, I put them in the PostGIS database and spatially indexed them:

$ /usr/lib/postgresql/9.1/bin/shp2pgsql -I -c AreaHydrography.shp nys_area_hydrography \
| psql -d gis > /dev/null
$ /usr/lib/postgresql/9.1/bin/shp2pgsql -I -c LinearHydrography.shp nys_linear_hydrography \
| psql -d gis > /dev/null

I wound up loading two layers for the linear features. One of them had the query condition:

name IS NOT NULL AND name != 'Stream'

while the other had:

name IS NULL OR name = 'Stream'

The reason for this was so that I could assign labels only to those streams not named 'Stream': that name appears on more than half the streams in the database!

I also did some styled lines for canals, intermittent streams, and so on. I'll put the QML files at the end of this post.

So now there is open water in my map. I still want to do some more hydrography, because my feet can get just as wet in mud! Swamps are important to indicate, too! Since the area that I'm immediately interested in mapping has no salt water, and since it's outside the Adirondack Park, the New York State Department of Environmental Conservation's list of protected freshwater wetlands should give me quite a reasonable starting point.

Those files are available by county. Downloading my county and several of its neighbours, I tried a quick import into QGIS and into PostGIS. For the E00 file format that was used, both imports failed silently, leaving a set of malformed polygons for the swamp areas. Fortunately, I was able to find a workaround. I used the program 'avcimport', part of the AVCE00 package, to convert the .E00 files into ARC/GIS binary coverages, and then used 'ogr2ogr' to import them:

$ for f in `find . -name \*.e0? -print` ; do ~/avce00-2.0.0/avcimport $f `basename $f .e00`-imp ; done
$ ogr2ogr -f "PostgreSQL" -s_srs EPSG:26918 "PG:dbname=gis" 001fwa-imp/ -nln nys_wetlands_arc arc
$ ogr2ogr -f "PostgreSQL" -s_srs EPSG:26918 "PG:dbname=gis" 001fwa-imp/ -nln nys_wetlands_pal pal
$ ogr2ogr -f "PostgreSQL" -s_srs EPSG:26918 -append "PG:dbname=gis" 057fwa-imp/ -nln nys_wetlands_arc arc
$ ogr2ogr -f "PostgreSQL" -s_srs EPSG:26918 -append "PG:dbname=gis" 057fwa-imp/ -nln nys_wetlands_pal pal
... continue for several more counties ...

Yet another task that I should have scripted!

Anyway, adding the resulting 'nys_wetlands_pal' and 'nys_wetlands_arc' in QGIS and doing a bit more styling gives quite an attractive result. I extracted an SVG of a swamp fill pattern and used that as the fill pattern for the polygons.

So now there is a lot of hydrography on the basemap. Next step is to start adding some cultural and administrative layers.

Post a Comment