Iteratively subsample a rater and reassemble
Ok, so I think the way I described may work for what you are doing -- basically, make a raster where each pixel is the per-country population value via ?subs linking the country code with the population. From that, you will have, for each pixel, an estimate for the full country population, and a corresponding ACTUAL population for each pixel, with which you can now do band math. Given a raster of two countries A and B: A A A B B B A A A A B B A A B B B B And data.frame: ID Population A 100 B 200 A ?subs will return a raster: 100 100 100 200 200 200 100 100 100 100 200 200 100 100 200 200 200 200 A more brute-force (assuming you have enough memory) is to ?getValues the entire raster, and convert it into a data.frame. For small rasters this is fine, for bigger rasters this is a more serious issue. --j
On Mon, Mar 31, 2014 at 12:12 PM, Gordon Holtgrieve <gholt at uw.edu> wrote:
Thanks for the reply Jonathan. I am actually trying to determine the relative population density spatially within each country, where the cell with the mean/median number of people set is to 0 (excluding cells with no population) and the variance from that is in units of SD. This is the same as the scale() function. I just want to do it on a per country basis rather than for the whole raster. Gordon On Mon, Mar 31, 2014 at 9:11 AM, Jonathan Greenberg <jgrn at illinois.edu> wrote:
Gordon: To clarify, you are trying to determine a relative population density per country, correct? I think you should look at the ?subs function, which will make it a lot easier to swap the country ID with the population value -- you just need a data.frame of ID and population. Then it seems if you create a new raster that has the population of the country for each cell, you can simply divide the per-location population by that raster. --j On Mon, Mar 31, 2014 at 12:12 AM, Gordon Holtgrieve <gholt at uw.edu> wrote:
Hello,
I have not worked with rasters much in R and am having a bit of trouble.
I have a raster of global population and a second raster of countries
identified by UN code (both at 1/2 degree resolution, but with different
extents). Ultimately I would like to end up with a raster where each
country's population is rescaled to N(0,1).
Can someone suggest the best way to do this?
So far I have been able to mask the population raster to a given country
and perform the rescale (with the plan to loop over countries) . I'm
stuck
on how to "reassemble" into a complete raster with all the countries.
#Code thus far -- although I'm sure there is a better way.
rasterCountriesUN[rasterCountriesUN != 840] <- NA #Mask countries not
of
interest
rasterCountriesUN[rasterCountriesUN == 840] <- 1 #replace the UN code
with
1
cropPop2010 <- rasterCountriesUN*rasterPop2010 # crop population data
raster
cropPop2010[cropPop2010>0] <- scale(cropPop2010[cropPop2010>0]) #rescale
cells > 0 (i.e., with people)
# I have other calculations to do here using the scaled population data.
###??? How do I store these results and move to the next country? Or is
there better way to go about this?
Many thanks,
--
Gordon Holtgrieve, Ph.D.
Assistant Professor
University of Washington
School of Aquatic & Fishery Sciences
1122 NE Boat Street
Box 355020
Seattle, WA 98105 USA
1-206-616-7041
skype: gholtgrieve
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-- Jonathan A. Greenberg, PhD Assistant Professor Global Environmental Analysis and Remote Sensing (GEARS) Laboratory Department of Geography and Geographic Information Science University of Illinois at Urbana-Champaign 259 Computing Applications Building, MC-150 605 East Springfield Avenue Champaign, IL 61820-6371 Phone: 217-300-1924 http://www.geog.illinois.edu/~jgrn/ AIM: jgrn307, MSN: jgrn307 at hotmail.com, Gchat: jgrn307, Skype: jgrn3007
-- Gordon Holtgrieve, Ph.D. Assistant Professor University of Washington School of Aquatic & Fishery Sciences 1122 NE Boat Street Box 355020 Seattle, WA 98105 USA 1-206-616-7041 skype: gholtgrieve
Jonathan A. Greenberg, PhD Assistant Professor Global Environmental Analysis and Remote Sensing (GEARS) Laboratory Department of Geography and Geographic Information Science University of Illinois at Urbana-Champaign 259 Computing Applications Building, MC-150 605 East Springfield Avenue Champaign, IL 61820-6371 Phone: 217-300-1924 http://www.geog.illinois.edu/~jgrn/ AIM: jgrn307, MSN: jgrn307 at hotmail.com, Gchat: jgrn307, Skype: jgrn3007