On Mon, 16 Feb 2009, Jim Burke wrote:
(Just stick to plain text, but don't use fonts or bold or stuff - keep it
simple).
I have a nice solid SpatialPologonsDataFrame and a new line file
(wkbLineString) called "major roads.shp".
MY QUESTIONS.
*I would appreciate examples of*
*a)How to merge the intersection of a **SpatialPologonsDataFrame and a
wkbLineString **
Why, and what do you mean? You have some 30000 road lines, what do you
want to know? How much of which road is in which polygon? Again, you need
to think through your workflow. My inclination would be to rasterise the
lines in a GIS, and overlay the raster cell centre points on the polygons,
but maybe you want line length, or to retain the line IDs (all 30000 of
them).
b)How to plot the result
You can of course overplot lines on polygons, with add=TRUE in plot()
methods and sp.layout= in spplot() methods. But plotting the result of the
"intersection" means what?
c)How to display the street name on the plot (that's FNAME from the major
roads.dbf file).
30000 names? Do you have a very large screen? Lines objects have IDs, but
no label point, so there is no easy way of doing it, even label alignment
is hard.
I can't actually see the statistical question here, could you please make
it clearer?
Do you simply want to plot a subset of the road lines on your solid
polygons, adding names? Then you need to find out how to subset them,
perhaps by cookie-cutting using the union of your polygons, add label
points and rotation angles (probably by hand), and off you go, but these
are essentially GIS operations.
Roger
*
ADDITIONAL INFORMATION.
The SpatialPologonsDataFrame is a garden variety collection of geographical
polygons.
tx1_sp <- readShapePoly("precinct08.shp", IDvar="PCT",
proj4string=CRS("+proj=aea +ellps=GRS80 +datum=WGS84"))
The new file to intersect merge is major roads line map that should overlay
part of my SpatialPolygons. It does not behave like a Shapfile.
main_roads <-readOGR("main roads.shp", layer = "main roads")
OGR data source with driver: ESRI Shapefile
Source: "main roads.shp", layer: "main roads"
with 29161 rows and 33 columns
Feature type: wkbLineString with 2 dimensions
Thanks,
Jim Burke
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--
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: [email protected]
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