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.
I think what you are trying to create is called
As it seems you do not have a supporting raster layer yet, it requires two steps.
- Create a raster from your points.
- 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)
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)
[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.