Complete the downloads documentation.

docs/components/custom-apps/web-app/dataset/downloads.md

 # Downloads
 
-## From API
+## From the API
 
-In the first section, the files are created by using the API.
+In the first section, the files are created by using the API (see [here](./api.md))
 
 ![Downloads query](../../../../assets/webapp/downloads.png)
 
-For example a PNG file is created by querying the WMS service with specific paramameters. Then the response is converted into a `blob` to allow the browser launch the download.
+Depending on the format and the dataset, it is possible to modify the localization (municipality) and the projection system.
+
+For each format, it may have 0, 1 or 2 parameters to download the file:
+
+* datasets with an `insee` code have the option to choose the municipality
+
+* for files retrived from services allowing multiple projection system as output (for example `WMS` or `WFS`), it's possible to choose the projection system
+
+* for a file format with no projection system (for example JSON of the non-standard `WS` service), and a dataset with no `insee` code, no option are provided
+
+Once the user clicked on the `Download button`, a file is created by querying the WMS service with specific paramameters. Then the response is converted into a `blob` to allow the browser launch the download.
 
 ## Static and other resources
 
 ![Downloads other](../../../../assets/webapp/downloads-2.png)
 
-Any other resources like static files (eg a `.csv` or `.tiff`) or an url are listed in two other sections as seen in the figure above.
\ No newline at end of file
+Any other resources like static files (eg a `.csv` or `.tiff`) or an url are listed in two other sections as seen in the figure above.
+These files are raw resources (document or link), and cannot be configured as the resources using the API.