I am trying to calculate volume using the GRASSplugin. I have my area information in vector format and my depth information in raster. I read that it is important to set the raster resolution before using GRASS. How do I know what resolution to use? My extent is currently the entire world for this project but it doesn't need to be.

Here is a tiff of the area I am working with: It is currently in WGS84 but I will save it as a custom CRS using lambert, centered at 70degrees:

enter image description here


Depending on your needs, the resolution usually should be such that a few thousand cells in both the X direction and the Y direction are sufficient. If you have map layers of the whole world then a resolution of 5 kilometers would give you about 8000 X 8000 cells in your raster. That's "comfortable". But, again, you have to clearly define your needs, and choose extent+resolution to meet your aims.

  • I have included a screenshot of the area I am working with. This Bathymetric data will be combined with habitat areas (shapefiles) in order to calculate volume. I will be using a custom CRS as I described above. Do you have any tips of what kind of resolution I need for what I want to accomplish? Also if I ever work with a larger area will I then need to reduce resolution that what I would use here? What are the effects of using the 'wrong' resolution? – anina Sep 23 '14 at 12:41
  • I don't think anyone outside your project can tell you what resolution to choose. It highly depends on your goals. If the custom projection uses meters, then start by checking the east-west and north-south extents. And, as I said, choose a resolution which leaves a few thousand cells in each direction. And if you switch to a larger area, you might certainly decide to change to a larger resolution. – Micha Sep 24 '14 at 21:00

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