brucap

How to extract information from a raster to a shapefile

Discussion created by brucap on Mar 4, 2012
Latest reply on Mar 6, 2012 by brucap
Hello everyone.

I'm a PhD student in economics and a newbie to ArcGIS, so forgive my incompetence.

I've the following problem. I've a raster dataset with information on the number of lightning on a 50Km x 50Km cell-grid over Europe.
The information comes actually from a ASCII file but I have no problem in converting into a raster dataset.
I also have a shapefile with the borders of all the provinces of Europe, and I can superimpose the 2 datasets correctly and define a common projection for the 2.

What I would like to do is to calculate the total number of lightning that fell in every province in Europe. Since not all the cells fall exactly within 1 province, I would like to weight the number of lightning contained in every cell by the % of area of this cell that falls within every province. In this way a cell were 3 lightnings fell in 2003 that is entirely within the province of Barcelona will assign 3 lightnings to Barcelona, while another cell with 3 lightnings that were only 1/3 over the province of Barcelona would assign only 1 lightning.
The final database to be exported would be one with 1 observation for every province in Europe and the corresponding statistics for lightnings attached to it.

What I can do now is to transform the raster dataset into a point dataset, and then ask a spacial join to compute summary statistics for all the cells whose center falls within any given province.
I don't like this procedure because not only does not allow me to weight less cells that do not fall entirely within a province, but also because it does not use the information of cells whose center does not fall within the province (but still cover part of the province).

I am not sure what I should do and with which tools or file types I should work.
I tried to Clip the raster with the shapefile but it could not use the raster as an input.
I also tried to compute Zonal Statistics as a Table (under the Spatial Analyst Toolbox), but the result is a table of only 1 row.
Finally, I tried to compute Zonal Statistics but ArcGIS crashed. I run ArcGIS with an ArcInfo licence for students, btw.

I hope to have made myself clear: let me know if I can clarify something.

Thanks a lot for the help!!

Bruno

Outcomes