Red Blob Games: How Google Maps' 2007 drag-and-drop routes led to a decade-long quest to explain differential heuristics

In 2007, Google Maps added a feature that let users drag route endpoints and instantly see recalculated paths. This hinted at a fast A* pathfinding optimization that author Amit Patel had never encountered. After studying the technique—differential heuristics—he spent over a decade trying to write a tutorial, failing repeatedly because he didn't understand it deeply enough. Switching to experimentation, he finally found a clearer explanation and released an interactive guide with new visualizations, including arrows showing heuristic mismatches and regions of improvement.