USA relief vector map in .CDR
Archive size: 7 Mb, zipped .CDR
License: Royalty Free
[Available in PDF and other formats: .DWG; .AI; .EPS; .CDR; .PPT.]
Being vector maps, they are completely editable, and scalable. No matter what big is the print size you need (office wall mural o bigboard). Zoom without quality degradation.
Please also check other vector maps of USA..
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This vector map of USA is available in different vector formats (the same price): .AI, .CDR .DWG, .DXF, .EPS, .PDF.
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USA relief map in vector. Cities and counties near
Our vector map of USA includes maps of the nearest areas (see the preview):
USA relief map for Corel Draw. Purchasing and downloading.
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Density maps using GDAL/OGR python Having a cloud of points is quite common. This tutorial shows how to calculate the density of points in a set of polygons.
As always, you can download all the data and scripts.
Seeking some data for the tutorial, I found the position of all the tornado touchdowns in the period 1950-2004. Calculating the “tornado density” in the US seemed interesting enough.
You can find the data at the data.gov site.
The density can be calculated in a regular grid or a set of polygons. We will do both things, using the US counties as the polygons, which I found at wingis.org
So the downloaded data looks like that when opened in QGIS:
It’s easy to see that most of the tornadoes occur in the east half of the USA, but it’s still difficult to see actual density differences.
Tornado density in every US county
First, a script to assign to every county a “tornado touchdown density” value. What the script will do is basically:
- Open the input datasets: The tornado points file, and the counties file
- Create the output file, and the fields we will use (name and state name, plus the density field)
- For each county, we use the method Within for all the points representing the tornadoes.
- We calculate the density. Since the file is in latlon projection, the GetArea method would be in square degrees, which is incorrect when comparing, because the actual area would be much smaller in northern regions.
So we re project the county geometry to the EPSG:900913 projection, which is in meters. I think that is actually incorrect, that the UTM would be better, but the zone changes too much and it’s out of the scope of the entry.
The density is simply the number of tornadoes divided by the county area.
- We write the output file.
Please visit this page for more details US states vector maps, ready for printing.