I have the following SpatialPolygonsDataFrame.
require(raster)
usa <- getData('GADM', country='USA', level=2)
metro <- subset(usa, NAME_1=="Nebraska" & NAME_2 %in% c("Dodge","Douglas","Sarpy","Washington"))
plot(metro)
I would like to be able to replicate the following map boundaries (defined by the colors):
Does anyone know a good plan of attack? I realize this is a somewhat manual process. I have already downloaded all US Census files that are of a more detailed geography. I was hoping that a more detailed level of geography could be aggregated to answer the above question, but unfortunately the districts do not line up the same.
Is there a R function already out there that would be helpful in assisting this manual process? At the very minimum, I would like to be able to leverage the perimeter of the 4-county area.
Use writeOGR from the rgdal package to create a shapefile of your metro object. Then install QGIS (http://www.qgis.org/), a free and open-source GIS, and load the shapefile as a new layer.
Then you can edit the layer, add new polygons, edit lines etc, then save as a shapefile to read back into R.
Additionally, you may be able to "georeference" your image (by identifying known lat-long points on the image) and load that into QGIS as a raster layer. That makes it easier to digitise your new areas. All you need for that is a few lat-long coordinates of specific points, such as the corners of polygons or line intersections, and then QGIS has a georeferencing plugin that can do it.
I don't think you'll find any R code as suitable for digitising new geometries over an image as good as QGIS.
After half an hour (and twenty years experience, not all of which you'll need) I've got this:
I didn't precisely digitise your new boundaries though, just roughly for speed. That QGIS screen cap shows the five coloured areas under the four metro areas.
Step one was georeferencing. This screengrab shows how the PNG has been georeferenced - the red line is the metro area shapefile drawn with transparency over the PNG after the PNG has been converted to a GeoTIFF by matching control points.
Step two was then using QGIS editing tools to split, join, and create new polygons. Then I just coloured them and added labelling to pretty it up.
I could probably bundle these files all up for you to neaten, but it really doesn't take that long and you'll learn a lot from doing it. Also, this is probably a gis.stackexchange.com question...
Related
Summary:
I'm trying to calculate the area of a large number of polygons in R. I've read a few posts about how I might do this (Example #1 & Example #2) but the problem I'm having is that my shapefile is too large (1.7gb) to import. Given I can't import the file, I can't calculate the area of the polygons.
Extended Explanation:
I'm actually trying to calculate the area of properties in Victoria, Australia. The polygons represent these properties. I downloaded the simplified models 1 and 2 of VicMaps from Spatial Datamart for all of Victoria.
However, given the size of the shapefiles, I had to narrow my search to just one local government area (LGA) and calculated the polygon areas (just for testing). The shapefile was 15.5MB.
library(raster)
x <- shapefile("D:/Downloads/SDM616230/ll_gda94/shape/lga_polygon/ballarat/VMPROP/PROPERTY_PRIMARY_APPROVED.shp")
crs(x)
x$area_sqkm <- area(x) / 1000000
This worked but its not a practical solution to my problem given there's many LGAs in Victoria and I plan to eventually follow the same process for Queensland and NSW.
However, trying to load a larger shapefile doesn't work and results in the below error code "Error: memory exhausted (limit reached?)".
I've tried using readShapePoly, readogr, st_read and read_sf to get the large shapefile into R but they don't work. I think the file is just too large. I tried using a select query within read_sf in an effort to reduce the size of the file I was reading but that didn't work either. I've read online that I should seek to split the shapefile into just the data I need to reduce the size - but I have no idea how to do that.
Hope you can help.
Obviously the file is too big for a single box. I think the options then are either
1) split the files into smaller ones, process one by one. See
https://gis.stackexchange.com/questions/195508/split-a-shapefile-into-smaller-files-on-linux-command-line
2) use some dbms or data warehouse to do it, they do such batching automatically.
I would like to use ggmap to plot several data points on top of a koppen-geiger climate map.
The kopper-geiger data and GIS/KMZ maps can be downloaded here:
http://koeppen-geiger.vu-wien.ac.at/present.htm
I've managed to have a code to plot the points on regular maps, obtained through the get_map function but I fail to use other maps such as koppen-geiger.
Any help will be appreaciated!
Your basic problem is that the map you are attmepting to use is an image file that is not georeferenced. So unless you want to go through the unnecessary and probably time consuming process of georeferencing this image yourself, you will be better taking an alternative approach. There are perhaps a few ways to do this. But, unless you have very few data points to overlay on the map which you can place manually using the lat-long grid of the image, then the least painful method will certainly be to redraw the map yourself using the shapefile.
This is not the right place to give you an introductory lesson on GIS, but the basic steps are to
Download shapefile (which is available at the same website as the image you linked)
Project map to desired coordinate system
Plot map, coloring by climate class
Color the ocean layer
Add labels, legend, and graticule, as desired
Overplot with your own climate data, and legend for these.
If you are unsure how to approach any of these steps, then take an introductory course on GIS, and search the Web for instructional materials. You may find this resource useful.
https://cran.r-project.org/doc/contrib/intro-spatial-rl.pdf
I have a scanned map from which i would like to extract the data into form of Long Lat and the corresponding value. Can anyone please tell me about how i can extract the data from the map. Is there any packages in R that would enable me to extract data from the scanned map. Unfortunately, i cannot find the person who made this map.
Thanks you very much for your time and help.
Take a look at OCR. I doubt you'll find anything for R, since R is primarily a statistical programming language.
You're better off with something like opencv
Once you find the appropriate OCR package, you will need to identify the x and y positions of your characters which you can then use to classify them as being on the x or y axis of your map.
This is not trivial, but good luck
Try this:
Read in the image file using the raster package
Use the locator() function to click on all the lat-long intersection points.
Use the locator data plus the lat-long data to create a table of lat-long to raster x-y coordinates
Fit a radial (x,y)->(r,theta) transformation to the data. You'll be assuming the projected latitude lines are circular which they seem to be very close to but not exact from some overlaying I tried earlier.
To sample from your image at a lat-long point, invert the transformation.
The next hard problem is trying to get from an image sample to the value of the thing being mapped. Maybe take a 5x5 grid of pixels and average, leaving out any gray pixels. Its even harder than that because some of the colours look like they are made from combining pixels of two different colours to make a new shade. Is this the best image you have?
I'm wondering what top-secret information has been blanked out from the top left corner. If it did say what the projection was that would help enormously.
Note you may be able to do a lot of the process online with mapwarper:
http://mapwarper.net
but I'm not sure if it can handle your map's projection.
I have a bunch of data on Dutch individuals that I would like to visualize with a choropleth map. I also have the location of the individuals (longitude and latitude), so I was hoping that it would be possible to visualize that on a Dutch map that is divided into municipalities (="gemeente" in Dutch), so I can color each municipality according to the mean value of all individuals living there. I know that the R package maptools can make choropleth maps, but I believe that it requires template maps in the form of a .shp file. Does anyone know where I could find such a template for the Netherlands? Preferably with municipalities and NOT per province, so for this image it would be the one on the left:
(source: www.kb.nl)
Any suggestions for other packages/software/etc to do this are also welcome! Many thanks!
also try GADM: http://www.gadm.org/
This site is an excellent resource, extra bonus: .Rdata is one of the formats you can download in (containing a SpatialPolygonsDataFrame). They also have .shp format, for your case.
Your main problem will be finding a shapefile for the municipalities. Once you have that and can easily relate your data at the lat/long level to the municipalities, then plotting becomes easy.
ggplot2 is a fantastic example.
Choropleths in R is a potential example, because it does not use shapefiles, but I believe the maps package supports it
Failing that, you could always try Weave
There are various .shp files for the Netherlands here:
http://www.eea.europa.eu/data-and-maps/data/eea-reference-grids/
You might also be able to find the municipalities layer on GeoCommons and join your data with one of those layers. GeoCommons makes it really easy to make many different choropleth maps quickly.
Another source for shapefiles at Eurostat is here. However, with a restrictive license, and I believe only at NUTS3 level (I did not look at it, though).
Open Streetmap does contain administrative boundaries,but not as polygons. Here is a report about how to transform boundaries to polygons. (I did not try)
You can find recent official Dutch maps here: https://www.pdok.nl/nl/producten/pdok-downloads/basis-registratie-kadaster/bestuurlijke-grenzen-actueel in .gml and .xsd formats (not in .shp unfortunately). National borders, province and municipality.
I have five shapefiles of bordering counties in California that I am trying to combine into one large shapefile and maintain the original borders of the counties. I then want to plot points such as this so the map only needs to be a simple map of county boundaries. Is there a way to do this in R or will I have to use something like ArcGIS?
There is extensive documentation about merging within a shapefile such as here where both shapefiles have the same coordinates. But no documentation on shapefiles that only partially share coordinates.
If you only need to put all the borders into one data set then you can do that with sp/rgdal easily enough, but if you need to actually merge borders geometrically (clip/join/dissolve) and so on the support in R is not that simple.
Roughly the simple option is read each shapefile with readOGR, then spRbind them together. If rgdal presents difficulties for building/installing then there are other options for reading shapefiles in various packages.
btw, "something like ArcGIS" but much closer to "free": www.manifold.net
If you are looking for a Free and Open Source solution I highly recommend QGIS or uDIG or OpenJump or MapWindows. You can do all the shapefile manipulation you want in these packages, they are all GIS software.
I am sorry I do not of a way to do this in R and I am not sure I would trust the result - better to use a hammer for a nail than to use a screwdriver.
If you want to programmaticly want to alter the shapefiles let me know and I will recommend some python and java libraries.