Physical Database Design & Entity Relationship Diagrams

When working with any relational database one must necessarily be concerned with the physical design of the database, and how that can be depicted visually in an entity relationship diagram (ERD).  The database entities must be related, or connected, by means of primary or foreign keys, and the attributes of each must be listed.  Working with spatial data, in particular, for use in a GIS, is done effectively with the use of PostGIS and SQL code.  Before the data is created or imported, however, it is typically beneficial to consider an ER diagram, in order to best visualize the data and database.  Below is a simple ERD with three entities- parcels, parks, and home sales, with the attributes for each listed as well.