I am new to QGIS, and I would like to know how I can create a raster colour map displaying (through colour) the minimum distance between each of the pixels of the raster and a set of geographic points (lat, long) stored in an ASCII file, so for instance if a pixel is right on top of one of the ASCII points would be green, if one pixels is 30 pixels (or by geographic distance) away from a point it would be red and so on.

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I think what you are trying to create is called Proximity Raster.

enter image description here

As it seems you do not have a supporting raster layer yet, it requires two steps.

  1. Create a raster from your points.
  2. Create a proximity raster from your point raster.

Let me assume you have a point raster (as above, left-hand side figure), with value 1 at your points and -99999 as background nodata.

Below workflow is only about the second step, to create a proximity raster.

From QGIS menu, open Raster | Analysis | Proximity (Raster Distance)

enter image description here

  • Input File: your point raster layer

  • Output file: please give a new filename

  • Values: any value assigned to your point (e.g. 1 for black dots)

  • Dist units: Pixel

  • No data: any background value (e.g. -99999 for white background)

    And hit [OK]. You can color the output raster as Singleband pseudocolor.

First step (to create a raster from ASCII point) is called Rasterize (vector to raster). To focus on proximity I did not touch on it, but you may have not done it before. If so, please search the topic on this site; there are many QAs about rasterize task.

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