First step on GIS with R

By tomizono

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The PM 2.5 checker written by R has been working nicely for me. I put a shortcut icon of this small script on my desktop PC, to check the air pollution when I run. The Ibaraki Prefecture Agency has been increasing watching points for PM 2.5 concentration from China. A problem is that I cannot picture to myself all the observation locations exactly.

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Fig. 1b. January 2016

Now, time to use the power of GIS.

1. Shape file

City boundary data is published by Japanese government agency at http://www.gsi.go.jp/kankyochiri/gm_jpn.html and http://www.gsi.go.jp/kankyochiri/gm_japan_e.html (English).

1. Download gm-jpn-all_u_2_1.zip (8MB) , which is the current (2015, v.2.1) file with all layers.
2. Unzip to ~/var/gis/gm-jpn-all_u_2_1, or somewhere you like.
3. The city boundary shape file is polbnda_jpn.shp.

Let’s see if this map data works or not.

Here I use CRAN package maptools.

library(maptools)
cities.japan 
A map of Japan is drawn. It's working.
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Fig. 2. City boundaries in Japan

I don't need the entire Japan but Ibaraki Ken local area only.
cities.ibaraki 
It's perfect!  The specification of data can be found at http://www.iscgm.org/gm/spec.html.
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Fig. 2. City boundaries in Ibaraki

This map is plotted with Longitude on X-axis and with Latitude on Y-axis.  The range can be shown by @bbox.
> cities.ibaraki@bbox
min       max
x 139.6879 140.85190
y  35.7396  36.94547

These values are useful to overwrite multiple layers on the same plot. Let's see the following plot fits exactly on the previous one.
plot(cities.ibaraki, add=T, 
     xlim=cities.ibaraki@bbox['x',], 
     ylim=cities.ibaraki@bbox['y',], 
     border=rgb(1,0,0,0.2), lwd=8)
Plot method is expanded for the class SpatialPolygons, and specific parameters can be found at the help page of SpatialPolygons-class.
Finally, I'm ready to  ...read more
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