I'm attempting to create a DEM from OS Terrain 50 data (ASCII Grid data) in QGIS.

The data is provided as multiple zipped folders representing sub divisions of OS grid squares. Each zipped folder contains an .asc file, a .gml file, and two .xml metadata files.

Dragging and dropping an .asc file into a layer gets me a DEM raster. The problem is that when I add adjacent .asc files, the created rasters don't blend. The edges have different brightness levels giving a tiling effect.

What am I doing wrong?

  • Each tile/layer/raster has its own range of values and thus its own symbology.
    – Erik
    Feb 5, 2020 at 13:36
  • Thanks. How do I combine them to make one seamless DEM raster?
    – flyhigher
    Feb 5, 2020 at 13:42

1 Answer 1


QGis is trying to be helpful by "stretching" the the "colours" of the tiles for you. The easy way around this to add all of the tiles as a single layer. This is quite easy as you can create a virtual layer so instead of this:

enter image description here

You can go to Raster->Miscellaneous->Build Virtual Raster, unclick place each input file into a different band and select all of your tiles as input. Giving this:

enter image description here

  • That's very helpful. Thanks.
    – flyhigher
    Feb 5, 2020 at 13:45

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