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1) The problem: I'm downloading layers for some work and I realized the elevation files (SRTM 90m) are displaced, I mean, the zero value is not the same I guess. I'm attaching photo below. They are technically all in 90m elevation.

enter image description here enter image description here

2) Specifications: I'm using Windows 10 and QGIS 3.16.2

3) Concernings I'm worrying maybe is a long answer, I'm beginner, I really don't know what to do to equalize the intervals (you can tell me the correct names to all the stuff I mention, like, the technical words on GIS)

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    Did you try to build a virtual raster or merge them? Right now each individual file is displaying their min/max values.
    – Gerardo Jimenez
    Commented Aug 25, 2021 at 17:24
  • thank you gerardo, i tried. I have another issue: once i do a virtual raster, is okey (well is whiter than expected, i dont know why, and Average, Highest and Lowest options on "resolution" they do the same) but once i try to save it (the virtual raster is a temporal file) the values change to double (but visually its okay) in the index table: from (-4,2543) to (-71, 4491)
    – Chiricaspi
    Commented Aug 25, 2021 at 18:25
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    As Gerardo mentions, this isn't a data problem, it's a display problem. You can right-click the layer, then "Styles" then click "Copy Style"->"Copy All Style Categories." Then you can paste that style into the other layer(s), which will ensure the same color scaling.
    – Jon
    Commented Aug 25, 2021 at 22:05

1 Answer 1

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Your raster seem correctly loaded.

Each of them has a different value/altitude range, for example:

  • srtm_68_14 has a minimum value/altitude of -43 and a max of 2160
  • srtm_65_14 has a minimum of -7 and a maximum of 4021

(The difference i.e. "maximum value - minimum value" is sometimes called the "dynamics" of a dataset.)

When files are imported into the project, QGIS tries to optimize the visual meaningfulness for each of them individually. In this case (one single value or "band", expressing altitude), by default QGIS assigns the color black to the minimum and white to the maximum, and intermediate grays to intermediate values (in a fashion called "linear interpolation" of the color ramp). So black in one raster does not show the same value as in another one.

This optimal/automatic assignement is good as it makes it possible (for us humans ;) ) to have an immediate idea about the contents of each file. When we want to analyze multiple adjacent images (aka "tiles", like in a moisaic) it is however better to have the same "color ramp" assigned to all layers. For example black can be assigned to the minimum value found across all layers, and white to the maximum, so we are sure that a given shade of gray has the same meaning (i.e. same absolute value) in all layers. When layers form a mosaic, this also has the advantage to create a visual continuum.

From what can be seen in your screenshots, the overall minimum is -43 (found in layer srtm_68_14), while the overall maximum is 4503 (found in srtm_65_13).

Let's create a suitable color ramp: double click on one layer, then choose Symbology on the left, and insert those values in the Min and Max fields:

enter image description here

This will change the "skin" (In GIS jargon the "Style") of the selected raster, making it less intelligible, but for a greater good. You can either repeat the Symbology step above for each layer, or copy the Style from the layer you just customized onto all other layers. To do so, right click on the layer's name:

enter image description here

Then right click on another layer, and select Style -> Paste Style.

You can even select mutliple/all (shift-click to select a range or ctrl-click to cherry-pick) layers and right click on them then select Paste Style.

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