This helps define what APIs and tools you’ll be looking at: maps, news, auctions, products, etc. Browse this site’s API Database and sort by Category to get a sense of API types. You can also browse the Mashup Listing to see which interesting applications have been built using which APIs.
So you want to make a mashup but aren’t entirely sure where to begin? This page can help you get there.
1. Pick a subject
Answer the question: a mashup of what? Hint: Plotting markers on maps is probably the easiest place to start. It might just be the best delis in your neighborhood. While you could go for something more complex with muliple data sources: maps + photos + bookmarks + more, you may want to keep it simple to start.