[R-sig-Geo] Intersect & Plot a Polygon and wkbLineString

[Roger Bivand]

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: Roger.Bivand at nhh.no