diff --git a/database/README.md b/database/README.md
index ba4572d..eb1d3ce 100644
--- a/database/README.md
+++ b/database/README.md
@@ -10,3 +10,5 @@ To use the builder, first install [shapelib](https://github.com/OSGeo/shapelib),
 This will create database files in `out` and `out_v1`, as well as a `db.zip` containing both directories.
 
 The files in the folder out\_v1/ use a newer format and use less space to encode the same information.
+
+The numbers in on the file names indicate the resolution. The `*21` file has a higher resolution for storing the borders, but it is larger. The `*16` file has a longitude resolution of 0.0055 degrees (~0.5km) and the `*21` file has 0.00017 degrees (~20m)