Topo Map

This page covers part 2 of my process for dealing with shapefile topography data from the National Map viewer in Leaflet.

• Part 1 - Topo Map (this page)
• Part 2 - Leaflet Topology Map

Inspired by this D3 sketch: http://bl.ocks.org/herrstucki/6312708

Github readme for that sketch here: https://github.com/interactivethings/swiss-maps/blob/master/README.md

Ultimate goal: map topo data from the National Map Viewer (maybe even automated somehow!)

National Map Viewer

http://nationalmap.gov/viewer.html

Downloading Shapefile Topo Data

Selecting a location for which I wanted topological data, I faced the dilemma of not knowing which data set to select.

I narrowed the view down to a specific region. I then clicked the download data link at the top.

I was presented with an array of choices, and I chose "Contour" data. This gave me multiple shape files, two of which covered the region of interest. I went through the checkout process to download these two shapefiles.

The region that I'm looking at is the Barry Goldwater Bombing Range outside of Yuma, Arizona, on the southwest Arizona-Mexico border.

Loading into QGIS

Here is what the shapefile looks like when loaded in QGIS... woah!

Converting

Shapefile to TopoJson

To convert this shapefile to something like TopoJson, I can use the TopoJson utility, which I installed as part of making my D3 Map (see http://charlesreid1.com/wiki/D3_Map#GeoJson_to_TopoJson).

Here is an example of a topojson call, from this page [1]:

topojson --id-property NR -p name=NAVN -p name -o NO_Admin_UTM33.topojson NO_Fylker_pol.shp NO_Kommuner_pol.shp

For my file, in the folder Elev_321166_Ajo_E_1X1/, I can convert the shapefile, Elev_Contour.shp:

$ topojson Elev_Contour.shp -o Elev_Contour.topojson -p
bounds: -112.99999999999994 32.00000000000006 -112.00000000013563 33.00000000086072 (spherical)
pre-quantization: 0.111m (0.00000100°) 0.111m (0.00000100°)
topology: 38071 arcs, 4228784 points
post-quantization: 11.1m (0.000100°) 11.1m (0.000100°)
prune: retained 38071 / 38071 arcs (100%)