If you ask me, if this was to be done, s the following steps should be taken.

1) The government should commission an expert panel to investigate a system for assessing land value (or perhaps even crowd source it). A set of descriptors (size, location, if it's next to a sewer treatment plant, etc.) should be determined. Along with sale price records, a system should be designed to predict land values.

B) Every part of the system should be public information, including the set of descriptors, so that individuals can dispute them and have them updated in the records.

C) Per law, the system should be regularly reviewed and updated, so that it is as accurate as possible.