Custom Choropleth value and color ranges

thanks @ressa on this
what you are asking and mentioning as possibile further features is already perfectly accomplishable with the actual version and architecture of the module.

As mentioned in the README.md file, the Leaflet Choropleth is founded on Drupal Plugin API system ( https://www.drupal.org/docs/drupal-apis/plugin-api → ):
indeed both its already embedded classification methods and color scales/ranges are just “Classification
“ and “ColorScale“ plugins types, as defined in the module
and that comply and implement the following interfaces:

- ClassificationInterface: https://git.drupalcode.org/project/leaflet_choropleth/-/blob/1.0.x/src/P...
that implements the generateBreaks(array $data, int $classes) method, returning an array …

- ColorScaleInterface: https://git.drupalcode.org/project/leaflet_choropleth/-/blob/1.0.x/src/P...
that implements the getColors(int $classes, bool $reverse = FALSE) method, returning an array …

Thus you should simply create your own custom module and implement (in the proper src/plugin/Classification and src/plugin/ColorScale folders) the new custom Classification and ColorScale plugins that you need to implement additionally, naming them the way you prefer, and returning (for those methods) the array(s) values that you want …
Of course in case of Classification plugin type you should return a logical array of incremental integer(s) or float values, while each ColorScale plugin type should return an array of hex color values …

You could start doing this simply copying and pasting from one of the plugins already implemented in the module in the following folders:
https://git.drupalcode.org/project/leaflet_choropleth/-/tree/1.0.x/src/P...
https://git.drupalcode.org/project/leaflet_choropleth/-/tree/1.0.x/src/P...

If correctly created those new custom plugins of you, with proper naming and adjusting their namespaces to refer to your custom module, you can bet they will be added and appear as additional options in the Choropleth Map Settings of the LC module.

For what concerns custom Legend labels (for each interval)
it is also already possibile to alter the %min and %max values (and also a fixed %value for Categorical use case) that are then passed to the Legend,
throughout the leaflet_choropleth_color_scale_alter hook
that is triggered here: https://git.drupalcode.org/project/leaflet_choropleth/-/blob/1.0.x/src/P...
and better documented in the leaflet_choropleth.api.php file,
where I also added a real use case that simulate the use case where we want to alter the Legend items values with fixed values …

For your and the whole community convenience I am attaching here a custom “leaflet_choropleth_custom” custom module that exactly implements all this scenario.

In particular it implements the following:
- a new classification “FiveBreaksOn0100” that creates 5 class equal breaks from 0 to 100;
- a new classification “Custom Issue 3537366" that created the exact classification breaks that you mention in this support request Issue #3537366
- a new color ranges “Fuchsias (Sequential)"

and also a leaflet_choropleth_custom_leaflet_choropleth_color_scale_alter function (in its leafle_choropleth_custom.module file) where the default legend_items values are replaced with $custom_values.

Once enabled that module and once set the “Custom Issue 3537366" classification, and “Fuchsias (Sequential)" color range and set the Legend Items format as the following:
“%min - %max - %value”

I am easily able to generate the attached Choropleth Map and related Legend based on those custom value breaks / intervals (that you mentioned above).

Hope all clear with this.

One thing that comes to mind, and that could be easily implemented/added, to avoid having to use the leaflet_choropleth_color_scale_alter hook (for defining custom labels for legend values), could be an additional long text configuration where the user enters the various values (labels) they want to associate with the different legend ranges (according to a specific requested pattern, such as each separated by a comma, a line break, or a pipe).
These values would then be translated by the %value placeholder into the Legend Items Format...
This is an improvement that's not difficult to implement in a future version of the module and would fulfill the Feature Requests of this issue even more easily (and with no custom code in your .module file).

Thanks @itamair for an epic explanation, much more than I could have hoped for. And thank you very much for the attention to detail, and even including a custom module example. It works perfectly, and I get the custom ranges, just like requested in the Issue Summary. Mille graze!

Based on your example and walk-through, I and anyone else interested in this, can absolutely now create our own custom Choropleth values and ranges.

About your thoughts of a future plans for a custom Color Scale (defining custom labels for legend values) via long text configuration, that could be a logical expansion to my suggestion in the Issue Summary, and I have extended the feature request with a new "combine value ranges, labels, and color scales" section.

If this "Custom" option is selected, the "Number of Classes" drop-down value should probably be disable (or ignored), since the number of elements are then in effect set. Also, if colors are set, the "Color Scale" drop-down value could also be ignored, I would think.

Add support for multiple Data Source Fields?

Another feature that would be awesome to have, is support for multiple Data Source Field's in a single View, since it looks like only a single Data Source Field is possible per View currently.

It's getting complicated though, and I am not sure what the best method would be ... I can think of two methods right now:

Scenario #1, Set source values in the Custom form

Could something like this work? (in a single form field or multivalue (paragraph-style) which ever is the least complicated to handle):

source: my_data_source_field
50-100|+50|#aa8c02
30-49.9|30-50|#cc4c02
25-29.9|25-30|#fe9929
23-24.9|23-25|#ffffd4

source: data_source_field_number_2
1000-10000|+1000|#aa9c82
100-999.9|100-1000|#cc4c02
1-99.9|1-100|#ffffd4

If this "Custom" option is used, the "Number of Classes" should probably be disable (or ignored), since the number of elements can vary.

Scenario #2, Paragraph-like "Add another"

Another solution could be to offer an "Add another"-button, which creates a complete extra "Choropleth Map Settings" below the current one, allowing an entirely different configuration for each Data Source Field.

Maybe that's better, since it retains the flexibility to use all the great configuration features? Then there would be no need to define a source key, and range, label, and color could be set for each data source, if so desired, and only this is needed:

50-100|+50|#aa8c02
30-49.9|30-50|#cc4c02
25-29.9|25-30|#fe9929
23-24.9|23-25|#ffffd4

One thing I forgot to include in my "Add support for multiple Data Source Fields?" suggestion above, is how to select which Data Source Field to use in the Leaflet View. So I'll add it, to keep it all in one place.