Each route zigzags through a few side-by-side columns of the grid, a column being the strip between two neighboring avenues: across one street, a block up the avenue, back across the next street, and so on. It goes north up one column and south down the next, so a neighborhood gets done in one visit, and an avenue is crossed only when moving to the next column. Each column is one line to remember, so there's no map to check. Routes are about 10 miles and start and end at a 1, 2 or 3 station where one is in reach (▶ marks the start, ■ the end). They're recomputed after each new run.