readOGR() - choice of layer in MIF/MID file?

Hello all,

[this is the continuation of a thread originally posted to r-help]

As recommended by Roger, I installed the rgdal package and went through
the description of my MIF/MID files. However, I was not able to load the
data using readOGR(), most probably because I did not manage to
correctly specify the layer. As I am pretty new to spatial data analysis
and R, I am still a bit lost. 

I tried with 
setwd("E\\Maps\\MIF")
test<-readOGR("testmif.mif", layer = "layer1")

and got the error message "Error in ogrInfo(dsn = dsn, layer = layer:
Cannot open layer"

testmif.MIF
testmif.MID
containing "points", "polygons" and "regions" and corresponding
attribute data. 
(R version 2.4.0 on Windows XP)

How to find out the correct layer name? The description file of the
MIF/MID file contains only descriptions of the attributes and elements,
but no explicit layer names. 

Katharina

****************************+

Katharina Frosch
Rostocker Zentrum
Konrad-Zuse-Str. 1
18057 Rostock
Tel.: (0381) 2081-148
Fax: (0381) 2081-448
Mail: frosch at rostockerzentrum.de 




-----Original Message-----
From: Roger Bivand [mailto:Roger.Bivand at nhh.no] 
Sent: Dienstag, 7. November 2006 20:47
To: Frosch, Katharina
Cc: r-help at stat.math.ethz.ch
Subject: RE: [R] wrong fill colors in polygon-map

On Tue, 7 Nov 2006, Frosch, Katharina wrote:

Dear Roger: Thank you for your help and the hint with the R-sig-geo

list

(next time I'll post directly to it)!

I went again through all points you mentioned: 
- polygons and rows of data are in the same order
- the number of polygons and data rows is identical
- I experimented with different values, and also defined explicit
breakpoints without using the quantile (no effect)
- then I added all.inside=TRUE in findIntervall (no effect)

However, adding the forcefill=FALSE option to the plot command led to

a

strange effect: three districts were left blank. Two of these

districts

were districts that are situated around another district (district
A=city itself, district B=the countryside around). The third

problematic

district is situated close to the Swiss border and next to a big lake.

I

deleted the three districts, to see what happens. The problem is

partly

resolved, but new blank districts appear. 

Could this be caused by a corrupted shape file rathern than by R? I
loaded the shape-file with the Program Mapviewer in MIF/MID format,
unionized some districts, then exported it to an ESRI-shapefile and

used

it in R. 

It is at least worth trying. May I suggest reading the MIF/MID file
directly into R using the readOGR() function in the rgdal package? If
you
are a Mac OSX user, there is extra help needed installing rgdal, but on
Windows it is available for binary install directly from CRAN (thanks to
Uwe Ligges). The spatial classes used there are more robust, and the
data
and polygons can be kept together. Polygons may also be dissolved using
objects of the SpatialPolygons class.

Could I suggest that you move any reply to R-sig-geo, given that the 
details of spatial data formats are not of general interest?

Roger

I don't have any clue to resolve this...so any hint is very welcome!
Katharina



**************************
Katharina Frosch
Rostocker Zentrum
Konrad-Zuse-Str. 1
18057 Rostock
Tel.: (0381) 2081-148
Fax: (0381) 2081-448
Mail: frosch at rostockerzentrum.de 

 


-----Original Message-----
From: Roger Bivand [mailto:Roger.Bivand at nhh.no] 
Sent: Dienstag, 7. November 2006 13:27
To: Frosch, Katharina
Cc: r-help at stat.math.ethz.ch
Subject: Re: [R] wrong fill colors in polygon-map

On Tue, 7 Nov 2006, Frosch, Katharina wrote:

Dear all,

I would like to produce a map with information about the patenting
activity in German districts, by coloring districts with different
degrees of patenting activity in different colors. I work with the
packages maptools, maps and spdep. The map data is read from an

external

.shp file (+ the corresponding .shx and .dbf files). Plotting a map

with

the IDs or the patenting indicator itself works fine. But coloring

the

map leads to completely odd results (wrong colors for most of the
regions). I also tried simpler values (just 0 and 1 for different
regions), same problem. I tried to check whether there is any

problem

with the match of data and district ids, but everything seemed to be
fine. 

Sample code: 
****************
brks.pat<-quantile(patenting$patbus)
#palette.pat<-c("green", "blue", "grey", "darkgrey", "red")
palette.pat<-c(rep("green", 4), "red")
plot(iab7.poly, col=palette.pat[findInterval(patenting$patbus,
brks.pat)])
legend(1200, -200, fill=palette.pat, legend=round(brks.pat,2),

cex=0.6)

title(main="patenting activity in german districts")

Data:
******
Iab7.poly contains the polygons of 343 German districts
patenting$patbus contains the number of corporate patents per

100.000

inhabitants for each district

(R-sig-geo may be a more focussed list for this kind of question)

If the polygons in Iab7.poly are in the same order as the rows of
patenting, and the number of polygons is the same as the number of

rows,

it is possible that the breakpoints are not quite what you think (if

for

example some of the quantiles are equal, which happens with
zero-inflated
data). Omitting all.inside=TRUE in findInterval() can also lead to the
insertion of NA values into the vector of colours.

Perhaps have a look at the classInt package for some examples of
choosing 
class intervals i.a. for map display.

Roger

Any ideas would be appreciated!

Best regards,
Katharina



******************************

Katharina Frosch
Rostock Center for the Study of Demographic Change
Konrad-Zuse-Str. 1
18057 Rostock
Tel.: (0381) 2081-148
Fax: (0381) 2081-448
Mail: frosch at rostockerzentrum.de 






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