Togaware DATA MINING
Desktop Survival Guide
by Graham Williams
Google

Spatial Data

R provides a set of tools for reading geographic (map) data, particularly ESRI shapefiles, and plotting and manipulating such data. Maps for many countries are available, particularly the US, Europe, and New Zealand. Only limited Australian map data is also freely available.



> if (!file.exists('australia.shp'))
  {
    download.file(paste("http://www.vdstech.com/mapdata/",
                        "australia.zip", sep=""), 
                  "australia.zip")
    system("unzip australia.zip; rm australia.zip")
  }

The data can be loaded into R with readShapePoly and displayed with plot. Australia has a few outlying islands which we crop from the main focus of the map here using Roption[]xlim and Roption[]ylim.



> library(maptools)



	Note: polygon geometry computations in maptools
 	depend on the package gpclib, which has a
 	restricted licence. It is disabled by default;
 	to enable gpclib, type gpclibPermit()

Checking rgeos availability as gpclib substitute:
FALSE



> aus <- readShapePoly("australia.shp")
> plot(aus, lwd=2, border="grey", xlim=c(115,155), ylim=c(-35,-20))

Image dmsurvivor-rdata:spatial_aus_map

The class of the resulting object (aus) is SpatialPolygonsDataFrame. Such an object has a collection of slots. For example, the data slot includes meta information about the region recorded in the data frame.



> aus@data



  FIPS_ADMIN GMI_ADMIN                   ADMIN_NAME
0       AS01   AUS-ACT Australian Capital Territory
1       AS02   AUS-NSW              New South Wales
2       AS03   AUS-NTR           Northern Territory
3       AS04   AUS-QNS                   Queensland
4       AS05   AUS-SAS              South Australia
5       AS06   AUS-TSM                     Tasmania
6       AS07   AUS-VCT                     Victoria
7       AS08   AUS-WAS            Western Australia
  FIPS_CNTRY CNTRY_NAME                REGION CONTINENT
0         AS  Australia Australia/New Zealand Australia
1         AS  Australia Australia/New Zealand Australia
2         AS  Australia Australia/New Zealand Australia
3         AS  Australia Australia/New Zealand Australia
4         AS  Australia Australia/New Zealand Australia
5         AS  Australia Australia/New Zealand Australia
6         AS  Australia Australia/New Zealand Australia
7         AS  Australia Australia/New Zealand Australia
  POP_ADMIN  SQKM_ADMIN SQMI_ADMIN  TYPE_ENG  TYPE_LOC
0    292475    2342.295     904.36 Territory Territory
1   6338919  803110.812  310081.09     State     State
2    161294 1352365.000  522148.09 Territory Territory
3   3107362 1733475.000  669294.69     State     State
4   1445153  985308.500  380427.59     State     State
5    472122   68131.477   26305.56     State     State
6   4354611  227781.406   87946.40     State     State
7   1655588 2533628.000  978233.81     State     State

The bounding box of the plot is available using bbox.



> bbox(aus)



        min       max
x 112.90721 159.10190
y -54.75389 -10.05139



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