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World Countries Poly to Raster

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#1
spesseh

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Hi again... :)

I am converting a world country shapefile into a raster. My raster cellsize will be 0.5 decimal degrees.
What i want to do is to have the country with the biggest area as the raster cell value.
This is quite basic by using the polygon to raster tool in ArcGis.
The problem is that small island states as Sao Tome among others will not be big enough to tranfser its value to the raster cell.
Any idea on how i can get the raster to keep these values instead of just converting it to 0 or ocean...?

Big thanks!
Andreas

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#2
frax

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Are your oceans non existant in the shape file, or have a value? I suspect they do, in your file, and maybe you need to delete the water polys first.

Another thing - what about small non-island countries, like Luxembourg, brunei and others?
Hugo Ahlenius
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#3
spesseh

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Are your oceans non existant in the shape file, or have a value? I suspect they do, in your file, and maybe you need to delete the water polys first.

Another thing - what about small non-island countries, like Luxembourg, brunei and others?


Thanks for your reply. I had to remove the water poly to be able to just keep land-area.
As you mention there will be a problem with some states dissapearing in this conversion. I am not sure what to do. It is important that each state has at least one cell as a geographical representation. This could of course be done manually, but is there any way of keeping at least one of each value? Any ideas?
Andreas

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#4
A. Fenix

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great question spesseh. my first thought is dependent on the fact that you do NOT have to have the cell size be 0.5 decimal degrees and that this is for a cartographic exercise, not a raster based analysis (i am assuming that you are choosing this cell size due to computer memory restrictions, etc). my first quick stab at something like this would be to select out the small countries and islands that have an area smaller than your raster cell size. I would then create two shapefiles; one for large countries and another for the small ones. i would then convert the large countries to the .5 dd, and then based off of the smallest area of your small country shp, convert to an appropriate cell value. at this time i would overlay the small raster layer over the big raster layer and then look what i have. i've never done this sort of thing before since i primarily only use raster for analysis...but just maybe this will meet your needs? anywho, it's the best i can when the sun is just peaking out and i'm on my third sip of coffee ;)

hope this helps...you along the way

Good Luck!
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#5
spesseh

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Your are on to something here i think.
The reason i want 0,5 dd cell size is that this is the unit of analysis which i want to work with. I am analyzing the contents of each cell, and extracts information from various datasets into my 0,5 dd vector grid.

I think your suggestion that i could overlay the small areas afterwards will solve it. Now i just have to decide on a limit on what areas shall be defined as "small neglected areas" :)

Cheers.
Andreas

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