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I would like to create a visualisation in QGIS that lights up raster points in a different colour. I have the rather points lit up but when I zoom out on the map, they look very small (they are 1km^2 in cell size).

Is there a way to make these dots appear bigger when zoomed out in QGIS?

enter image description here

Scale in visual is at 1:34,569,229

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    You might want to look into converting your raster into a vector points data set, then deleting all the points that are the code for white. – Spacedman Mar 21 '18 at 13:41
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Starting with a spotty raster like this, where 1 is a black square and 0 is elsewhere:

enter image description here

Use "Polygonize", and then deleting the code=0 polygons gives me this:

enter image description here

which is all the pixels outlined as polygons. If adjacent pixels are 1, then the whole block is outlined.

Then use "Centroids" to make a point at the centre of each polygon:

enter image description here

Note how there's one point assigned that that block on the upper left which was two pixels (sorry things don't line up exactly).

If I overlay the points and the original raster you can see this more clearly:

enter image description here

If that's what you want then job done, I can't see a direct way of turning every pixel into a point, but I'm sure it can be done if that's what you actually want.

Once you converted to points, you can style them and they can be a large and constant symbol size. You can even make them square symbols if you want, but they'll be centred on your original pixels.

If you want every pixel to have its own point, then save the raster in XYZ format, which results in a text file of X,Y values for every grid cell with an extra column of the pixel value. This can then be read in as a vector points delimited text data file.

See:

https://www.slideshare.net/shencoop/qgis-raster-to-point

for more, although recent versions of QGIS look a bit different. The crux is saving as a file with a .xyz extension so that GDAL uses the XYZ output driver.

  • Thanks, I used GRASS r.to.vect as a solution, but had to remove null values to get the computational time down. Worked well. – Lucy Mar 22 '18 at 7:09
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Thanks for the help. The solution I used is below:

QGIS - extract raster values greater than 0 to extract raster values that are non-zero and remove all 0 values from the data (greatly improved processing time for the vectorization)

I had a bug with one of the raster-to-vector tools, and ultimately used GRASS > r.to.vect, feature type area and use raster values as categories, which worked really well.

Then changed the border size of the vector to be able to view this zoomed out.

See below:

enter image description here

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