diff --git a/API.md b/API.md
index 8b990cb90..55972a4fb 100644
--- a/API.md
+++ b/API.md
@@ -8,7 +8,7 @@ iD supports several URL parameters. When constructing a URL to a standalone inst
 of iD (e.g. `https://ideditor-release.netlify.app`), the following parameters are available
 **in the hash portion of the URL**:
 
-* __`background`__ - The value from a `sourcetag` property in iD's
+* __`background`__ - The value of the `id` property of the source in iD's
   [imagery list](https://github.com/openstreetmap/iD/blob/develop/data/imagery.json),
   or a custom tile URL. A custom URL is specified in the format `custom:<url>`,
   where the URL can contain the standard tile URL placeholders `{x}`, `{y}` and
@@ -383,4 +383,4 @@ A "name" field must be included:
     "label": "Name",
     "placeholder": "Common name (if any)"
 }
-```
\ No newline at end of file
+```