In 2012 good friends of mine embarked on a motorcycle trip around the world, although I did not create their website (ridetheworldtogether.com) I helped with many small features such as a RSS feed reader which automatically populates any YouTube updates, as well as an interactive map showing their route so-far.
At first I used existing services such as EveryTrail and TripTracker which started to really slow down the map navigation as their route became much longer. I eventually took matters into my own hands and created a system using PHP and MYSQL to read GPX (xml based GPS files) and populate a database with time, coordinates and other info.
I also learned how to use Google Map's API to display a very complex route on a map using data compression as the line plots loaded onto the map exceeds 650,000 points so far. I also created a crude GUI so that all my friend needs to do, is upload the GPX files and press a button to load the points into the database.
PHP
Google Maps API
SQL
AJAX