Add .gitignore, ignore editor files
Remove some dead code/markup
Hoist the JS to the head & tidy slightly
Bump OpenLayers to 2.13.1
tidy -config tidy.conf index.html

Since it's HTML5 you will need https://github.com/w3c/tidy-html5
Use a <header> tag for the hero
CSS - use shorthand properties
Age perl a bit