2

I have two shapefiles

  1. Administrative boundary
  2. Stream extract flow (using r.stream.extract)

and Raster DEM file

I want to find lowest elevation point in each administrative polygon and this point should also be present on stream extract flow

Image 1 shows when stream_flow vector file is taken with polygon shapefile along with DEM

Below image shows when stream_flow vector file is taken with polygon shapefile along with DEM

Image 2 shows when stream_flow raster file is taken with polygon shapefile along with DEM

Below image shows when stream_flow raster file is taken with polygon shapefile along with DEM

5

You can achieve what you want in two steps:

  1. You need to extract the values of DEM raster data into point shapefile using QGIS Point sampling tool. You need to make sure that the raster data and the point shapefile have the same projection. If the raster data and point shapefile have different projections, the output point shapefile will have empty fields for the values of raster data.

  2. Use intersect tool from Vector -> Geoprocessing Tools -> Intersect to intersect the points with DEM values with the polygon boundary to get the points classified by boundary. At this level you can get the lowest point within each boundary.

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  • Thanks. Is it possible with python script to find lowest elevation point for each polygon (Long and Lat) (This point should be intersection of point lying on boundary of polygon shape file and stream extract flow vector file)
    – sudhanshud
    Jul 6 '17 at 11:07
  • If you want to use python for this task, you have to include a python code snippet first, what have you tried and where did you stuck. Without writing your python code, your question will likely to be closed as off-topic.
    – ahmadhanb
    Jul 6 '17 at 11:13
  • Hi. Sorry for not providing code. I am newbie here and I don't know any python library function for QGIS and I have to find lowest elevation for each polygon
    – sudhanshud
    Jul 6 '17 at 11:28

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