I wanted to know how can I calculate land/sea area ratio in a portion of raster map (attached in the mail) Till now i had this raster map that i converted in to vector by the option raster>>conversion>>polygonise then i install the plugin CATOGRAM to draw grids. However i get no output.
An easiest way to calculate the land/sea area is to do the following:
- Download the shapefiles of administrative boundaries of Malaysia and Indonesia from gadm
- Merge the two shapefiles together to have them in one shapefile
- Create a new rectangle shapefile to clip the merged polygon shapefile
- Use Union tool to union the clip polygon with the clipped administrative shapefile resulted from the previous step.
- You will have a new shapefile that represents a land and a sea,and you can calculate their areas. But before doing that, don't forget to project the output from the last step to a suitable projection in meter like (UTM) before calculating the area.