newbie questions

Hello all:

I'm trying to make some simple maps of election results and I am having
some trouble.  I'm hoping to use Grass (or QGis) to make the maps, but
apparently this requires getting my data into the shape files, and I
can't figure out how to do that.  I've found read.shape and that's

great, and I thought that by editing the resulting att.data data frame I
could do what I need.  Unfortunatly, if I use merge to combine my data
with the existing data, the data frame comes out sorted by the join
column and the output dbf file (done with write.dbf) doesn't work
properly with the shapefile because it's no longer sorted the same as
the outlines.

I tried preserving the original order of the data frame and re-sorting
the data frame before writing it out, and that worked, but the resulting
dbf file causes a seg fault in Grass when I try to read it with the rest
of the shape data.  Plus it seems a ridiculous amount of work for what
must be a fairly routine operation.

So here's my question: I have some data I want to add to a shape file
(the SHP, DBF, etc).  Can I use R maptools to do that easily, and if so,
how?

Many thanks in advance for the help,

-tom

I'm trying to make some simple maps of election results and I am having
some trouble.  I'm hoping to use Grass (or QGis) to make the maps, but
apparently this requires getting my data into the shape files, and I
can't figure out how to do that.  I've found read.shape and that's

Please do not use read.shape(), it is deprecated, and will become
unavailable at the user-visible level at the next maptools release.

Do use readShapeSpatial() (or better readOGR() in rgdal) to create a
SpatialPolygonsDataFrame, paying attention to the ID= argument. Then
use spCbind() and if necessary spChFIDs() to ensure that your data are
being associated with the correct Polygons object inside the
SpatialPolygonsDataFrame. Then use writeSpatialShape() (or writeOGR())
to write the shapefile.

great, and I thought that by editing the resulting att.data data frame I
could do what I need.  Unfortunatly, if I use merge to combine my data
with the existing data, the data frame comes out sorted by the join
column and the output dbf file (done with write.dbf) doesn't work
properly with the shapefile because it's no longer sorted the same as
the outlines.

Using merge() without reading the help file usually has this outcome - 
there are arguments controlling sorting.

PS. Did you read the Spatial task view on CRAN, or, say, the page on
the R wiki entitled "Getting spatial data into and out of R":

http://wiki.r-project.org/rwiki/doku.php?id=tips:spatial-data:import_export

I tried preserving the original order of the data frame and re-sorting
the data frame before writing it out, and that worked, but the resulting
dbf file causes a seg fault in Grass when I try to read it with the rest

must be a fairly routine operation.

So here's my question: I have some data I want to add to a shape file
(the SHP, DBF, etc).  Can I use R maptools to do that easily, and if so,
how?

Many thanks in advance for the help,

-tom

-- 
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

Hi Tom!

I'm a geographer and R enthusiast too, but what I can say is: R is a great
software to statistics. The final production of maps, although it's
possible, it's simple and faster made with GIS softwares, like GRASS,
Quantum GIS or ArcGIS.

My tip is: organize data with spreadsheet and GIS softwares, import (as
shapefile, if possible) in R and make your statistical analysis and
statistical columns of data, export to another shapefile and manipulate the
final map in GIS softwares.

I repeat, it's possible make all these steps in R, and generate great maps,
but the most simple way is above. Personally, I use R to make the final maps
only when I have to produce a long series of simple maps.

I think the best way is the integration of GIS software with R, each one
with his specialty.


King regards,

Raphael Saldanha
BRAZIL
saldanha.plangeo at gmail.com

	[[alternative HTML version deleted]]

Do use readShapeSpatial() (or better readOGR() in rgdal)

Hi Tom!

I'm a geographer and R enthusiast too, but what I can say is: R is a great
software to statistics. The final production of maps, although it's
possible, it's simple and faster made with GIS softwares, like GRASS,
Quantum GIS or ArcGIS.
  

My tip is: organize data with spreadsheet and GIS softwares, import (as
shapefile, if possible) in R and make your statistical analysis and
statistical columns of data, export to another shapefile and manipulate the
final map in GIS softwares.

I repeat, it's possible make all these steps in R, and generate great maps,
but the most simple way is above. Personally, I use R to make the final maps
only when I have to produce a long series of simple maps.

I think the best way is the integration of GIS software with R, each one
with his specialty.


King regards,

Raphael Saldanha
BRAZIL
saldanha.plangeo at gmail.com

	[[alternative HTML version deleted]]

... In addition, I use linux (Debian) and the desktop GIS tools that
I tried (svSig, Qgis, and some more) did not provide publication quality
maps.

On Sun, 15 Nov 2009 19:52:48 +0100 (CET) Roger Bivand
<Roger.Bivand at nhh.no> wrote:

Do use readShapeSpatial() (or better readOGR() in rgdal)

Why (or how) is readOGR better?

Roger Bivand <Roger.Bivand at nhh.no> wrote:

I'm trying to make some simple maps of election results and I am having
some trouble.  I'm hoping to use Grass (or QGis) to make the maps, but
apparently this requires getting my data into the shape files, and I
can't figure out how to do that.  I've found read.shape and that's

Please do not use read.shape(), it is deprecated, and will become
unavailable at the user-visible level at the next maptools release.

Where is the introduction that explains all this?  Is there one
somewhere?   (And thank you for the assistance.)

Do use readShapeSpatial() (or better readOGR() in rgdal) to create a
SpatialPolygonsDataFrame, paying attention to the ID= argument. Then
use spCbind() and if necessary spChFIDs() to ensure that your data are
being associated with the correct Polygons object inside the
SpatialPolygonsDataFrame. Then use writeSpatialShape() (or writeOGR())
to write the shapefile.

Thank you very much for all that, it gives me a lot to try.

great, and I thought that by editing the resulting att.data data frame I
could do what I need.  Unfortunatly, if I use merge to combine my data
with the existing data, the data frame comes out sorted by the join
column and the output dbf file (done with write.dbf) doesn't work
properly with the shapefile because it's no longer sorted the same as
the outlines.

Using merge() without reading the help file usually has this outcome -
there are arguments controlling sorting.

Thank you for the help, but no thank you for the snide.  What the help
file says (on my system) is that if you do sort=FALSE, the output order
is unspecified, which is approximately zero help for someone trying to
figure out why the output map looks so funny.

PS. Did you read the Spatial task view on CRAN, or, say, the page on
the R wiki entitled "Getting spatial data into and out of R":

http://wiki.r-project.org/rwiki/doku.php?id=tips:spatial-data:import_export

Yes.  I can't say I found those pages very helpful since they are mostly
written in a language I don't understand, and where I do understand what
they're saying, they're saying things like this:

"Use a GIS if you're trying to do the following:

   - specialized GIS tasks"

In the nicest and most constructive way I can think of, I have to say
that this isn't very helpful to the person who has data they want to map
and wants to get on with it.  I have been a R user (and fan) for years
and am more or less familiar with much of it, but I haven't used it for
spatial data, and I find the available documentation for people who are
starting from zero like me is fairly wanting.

Many thanks,

-tom

I tried preserving the original order of the data frame and re-sorting
the data frame before writing it out, and that worked, but the resulting
dbf file causes a seg fault in Grass when I try to read it with the rest

b> > of the shape data.  Plus it seems a ridiculous amount of work for what

must be a fairly routine operation.

So here's my question: I have some data I want to add to a shape file
(the SHP, DBF, etc).  Can I use R maptools to do that easily, and if so,
how?

Many thanks in advance for the help,

-tom

--
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

Including a code snippet demonstrating your problem and posting a link
to a simple data set (shape file plus election data) would be a more
constructive way to proceed, no? The code in Ch 5 in our book on
www.asdar.org covers a very similar case, 

... In addition, I use linux (Debian) and the desktop GIS tools that
I tried (svSig, Qgis, and some more) did not provide publication quality
maps.

I would strongly suggest you take another look at some of these
packages (especially QGIS).
These are relatively young projects, and are growing (changing)
quickly. For example, just
recently, some very advanced symbology enhancements have been made to
the QGIS project,
and will likely be available in the next release (due out next month).
Though of course, for graphs
and other statistical outputs, nothing beats R!

Carson

On Monday 16 November 2009 08:53:03 Carson Farmer wrote:
  

... In addition, I use linux (Debian) and the desktop GIS tools that
I tried (svSig, Qgis, and some more) did not provide publication quality
maps.
      

I would strongly suggest you take another look at some of these
packages (especially QGIS).
These are relatively young projects, and are growing (changing)
quickly. For example, just
recently, some very advanced symbology enhancements have been made to
the QGIS project,
and will likely be available in the next release (due out next month).
Though of course, for graphs
and other statistical outputs, nothing beats R!

Carson
    

Let me strongly second Carson's points. As a Debian user, I like QGIS and use 
it for my own visualization purposes. Being able to drag and drop a shapefile 
is pretty awesome. I suspect QGIS will continue to improve in its ability to 
render maps. That said, I don't think publication-quality output is what these 
software are about, at least not yet. R on the other hand gives you tremendous 
control. I used it exclusively for all maps, as well as other graphics, in my 
latest article.

The same goes for non-free GIS software, by the way. My cartographer 
colleagues who use ArcGIS generally haul mapping output from there into other 
packages for font and other effect rendering.

Yours,

Ashton