update @id notes

book/thematics/docs/maps.md

@@ -44,6 +44,13 @@ indicate the type of document it is through a mimetype via encoding.
 :linenos:
 ```
 
+```{tip}
+@id around line#6 should point to whatever resolves eventually to the JSON-LD - if you only
+have an external JSON-LD file (and not embedded into the html `<script>` tag)
+then the @id should point to the .json file itself. Otherwise, @id should point
+to the landing page of the record (HTML page), that embeds the JSON-LD.
+```
+
 
 ```{code-cell}
 :tags: [hide-input]