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I am aware that how to convert a vector layer to a raster layer is a quite frequent problem and that there are many questions and answers dealing with it. However, none was helpful concerning my specific problem, so I hope it's okay to ask again. I have a huge dataset consisting of fish catch data - different species and the location where they were caught. The original data is a csv file, but I'm working with it in QGIS and have created a vector file from the spreadsheet. Now I want to use another program (Zonation) that only accepts raster files to calculate species richness in certain areas - is there a possibility to create a raster from a vector layer with irregular points? I have tried the Rasterize tool, but it only gives me a solid rectangle and all individual data points are lost. I'm working with CRS WGS 84 and I have tried to set the cell size to 0.4, but still it's only one solid square. I've never worked with raster files before and I'm very grateful for your help - thanks!

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You need to chose an interpolation algorithm which is suitable for your input data. –  underdark Sep 26 '13 at 17:39
Where can I do that? –  Kristina Sep 26 '13 at 17:40
Sorry, I meant check the literature for which data to use to interpolate fish catch data or similar. I assume it's a common step in papers in that field but it's not my research area. Just wanted to give you the pointer that you need to look for "interpolation" –  underdark Sep 26 '13 at 17:43
Good to know, found the tool but am unsure how to work with it - it's a bit confusing that it asks for an interpolation attribute and I don't know what to put in there. –  Kristina Sep 26 '13 at 17:47
And thanks so far! –  Kristina Sep 26 '13 at 17:47

1 Answer 1

It is not clear from your question what format the "other program" expects. 1) A "binary" raster with the value of the catch in cells with recordedcatch, and zeros elsewhere? 2) A raster with interpolated values of fish catch? Or 3) something else?

Case 1:

  • Add the points as a layer in QGIS.
  • Go to Raster->Conversion->Rasterize
  • As input file,select the point layer, as attribute field,select the values you want at the "catch points".
  • Give the output file (raster) a name,and select a fileformat.
  • Select the size/resolution of the output raster and run. The output raster now has the values of the catch in the cells, and zeros where there was no catch recorded.

Case 2:

  • Add the points as a layer in QGIS.
  • Go to Raster->Interpolation->Interpolation
  • Under "Vector layers", select the point layer, under Attribute, select the values you wish to interpolate (e.g. Catch) from the point layer.
  • In the "Output" box, use TIN as a first go, and select an appropriate cellsize for the raster.
  • Name the output file (will be a raster with .asc extension)
  • Help for the tool is here: http://www.qgis.org/en/docs/user_manual/plugins/plugins_interpolation.html

Case 3: You need to provide somemore details, but you might end up with one of the tools described above.

For general vector->raster operations, see How to convert a vector layer to raster?.

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