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I have a dataset that shows the borehole yield for fractured aquifers in South Africa. Using the "yield_ls" column, my CARTO VL legend looks like this (notice how the 4th item should be the first).

const aquiferViz = new carto.Viz(`
  color: ramp($yield_ls, teal)
  strokeColor: rgba(0,0,0,0.3)
  strokeWidth: 1
`);

enter image description here

I noticed that each legend item is assigned an ID column in the database ("sayld_id") starting from 6 to 10. Therefore if this database is ordered by the sayld_id ASC, then the yield_ls features go into a logical order. I tested this using the following SQL command in my CARTO dataset:

SELECT *
FROM fractured 
ORDER BY sayld_id ASC   

enter image description here

I then tried to do this when adding my the layer to a CARTO VL map using:

const fracturedSource = new carto.source.SQL(`
  SELECT *
    FROM fractured
    ORDER BY sayld_id ASC
  `);

But the legend remains the same as before. Is there a better way to correctly arrange the legend, or possibly move an item up or down in the legend order?

3

I think the problem here is that you're passing directly the attribute ($yield_ls) to the ramp expression, and the results are sorted by number of occurrences of each category.

In order to classify the content you're receiving, you've to use the buckets as follows:

color: ramp(buckets($yield_ls, [
    "Fractured 0.0 - 0.1 l/s",
    "Fractured 0.1 - 0.5 l/s"
    "Fractured 0.5 - 2.0 l/s"
    "Fractured 2.0 - 5.0 l/s",
    "Fractured > 5.0 l/s"
]), teal)

In this case, $yield_ls is a categorical attribute, you have to make sure that all the values passed to the buckets expression ("Fractured ...") match perfectly with all the category names you want to classify.

  • Thanks Elana, this is exactly the solution I was looking for! However, although I have listed the 5 buckets for each categorical attribute that exists in the dataset, I am getting a "CARTO_VL_OTHERS' item in my legend. This is strange because there are no other attributes in my dataset. Is there a way to remove this from the legend? – JohnGIS Feb 22 at 10:43
  • 1
    I think you're right, when building the legend data for the buckets expression, if the attribute is categorical, we're always adding the 'others' data. I'm going to open an issue to check this, thanks for reporting it! Meanwhile, you can show all the values except the one with the CARTO_VL_OTHERS label. – Elena Torró Feb 22 at 11:01
  • Issue in GitHub: github.com/CartoDB/carto-vl/issues/1273 – Elena Torró Feb 22 at 11:10

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