title: How do I change blank OpenStreetMap tiles to be classified as water using PostGIS and GeoServer?
body: <p>I'm following these two tutorials: (1) <a href="https://learnosm.org/en/osm-data/osm2pgsql/" rel="nofollow noreferrer">LearnOSM</a> and (2) <a href="https://github.com/fegyi001/osmgwc/blob/fa6130469a491446e75a33e778143eee5ebbfdaa/README.md" rel="nofollow noreferrer">OSMGWC</a>. They cover OpenStreetMap, PostgreSQL + PostGIS, and GeoServer. </p>
  
  <p>I've downloaded an extract of a state from <a href="https://extract.bbbike.org/" rel="nofollow noreferrer">extract.bbbike.org</a>. I have all the layers configured together and the map looks perfect except for one thing: there's no surrounding ocean tiles. It's all white.</p>
  
  <p>I'm thinking I could just replace all empty tiles with water tiles, and that would solve my problem. How can I do that? Or, if my idea sucks, what should I do instead?</p>
  
  <p><a href="https://i.stack.imgur.com/7FBAy.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/7FBAy.png" alt="It&#39;s all white"></a>.</p>