Where can I get the x, y, z -coordinates for California to use a contour plot?

Question

I would like to make California's map by the contour plot. However, I do not know how to get the necessary x, y and z -coordinates.

Answer 1

Have you consulted the California's Geospatial Information Office? There's also geodata.gov, which links to a bunch of elevation datasets, including the USGS National Elevation Dataset.

Answer 2

The GDAL library (www.gdal.org) has many useful commands for processing these types of data. Most elevation data formats, such as those available through the national map server: http://nationalmap.gov/viewer.html are readable by GDAL. The command gdal2xyz.py can read these rasterized files and write X,Y,Z triplets. Or you can skip straight to rendering contour lines with gdal_contour. The excellent cross-platform GIS software Quantum GIS (www.qgis.org) is also very useful for processing geospatial data, and includes menu-driven access to most of the functionality of GDAL.