+Run this command in the db/functions directory:
+
+$ make libpgosm.so
+
+You might also need to install:
+- postgresql development libraries: $ sudo apt-get install postgresql-server-dev-8.3
+- ruby development libraries: $ sudo apt-get install ruby1.8-dev
+for build to succeed.
+
+Now create the function as follows:
+
+$ psql openstreetmap
+(This may need authentication or a -u <dbowneruid>)
+
+> CREATE FUNCTION maptile_for_point(int8, int8, int4) RETURNS int4
+ AS '/path/to/rails-port/db/functions/libpgosm.so', 'maptile_for_point'
+ LANGUAGE C STRICT;