Labelling contour lines in QGIS?

Question

I need to label contour lines in QGIS 2.14. I've tried a few things, including Choosing only one contour line to label in QGIS? but it labels with the IDs instead of altitude.

EDIT: I've created the contour lines using this method : loaded an MNT (RGEALTI from IGN in France that contains altitude data), then menu raster / extraction / contour Here's the MNT image:

Labels window:

![enter image description here

EDIT: using ELEVATION instead of ID doesn't display the altitude

EDIT: I went again through the process of extracting contour lines (raster/extraction/contour lines) but this time I added a name to the attribute as suggested below by Gabriel C. And there is an error during the process. Here's the attribute table of the layer:

Answer 1

I feel the error comes from your contour generation. If you didn't set an elevation attribute name, the attribute gets skipped and you have no way to define what elevation your contours are at. Make sure the name respects shapefile requirements (no accents, no spaces, maximum 8 characters) to avoid problems.

Answer 2

Change this to your Height-Attribute:

Answer 3

Contour lines usually have a field in the attribute table where the elevation data is stored. You would then select this attribute from the dropdown menu where it says "label with" or "etiquette avec." Et voilà, the contour lines are labeled with elevation data.

Unfortunately, the elevation data is missing from your contour lines. There's nothing you can do with this layer to make it display elevation, because that information simply isn't there. You could add it yourself by adding a topographic basemap and editing the attributes of every single topoline to match the basemap, but that's a last resort. Instead, try one of the following:

• Try to find contour lines from a different source. You may be able to download a contour layer for free. This question on OpenData SE may help you find topolines for your area of interest.

• If contour lines aren't available for free, you should be able to obtain a DEM (digital elevation model) raster. Use the DEM to create contours.

• If you need contours which are identical to the contour layer you already have, try this approach. Convert the contour lines to points using the extract vertices tool, then add the elevation data to those points using the point sampling plugin or Add raster values to point tool. See here for more information. Then add an attribute to the original contour layer which takes the rounded average of the elevation of all the points, using an expression like this:

   round( aggregate('pointlayer', 'mean', "elevation"), -1)
  

  Substitute your own point layer name and elevation attribute name where the expression says 'pointlayer' and "elevation".