The bus map with torn strips, and the streets we kept guessing
At dawn in the bus depot, I spread my route map on the dash. Old tears left blank strips, so I’d been steering by memory through the missing blocks. A human DNA reference used to be like that map: a main guide with stubborn gaps. I wanted one sheet with every street drawn, end to end.
The blank strips sat where the city gets tricky: lookalike estates, tight loops, roundabouts that all feel the same. In human DNA, the hardest gaps were the most copy-and-paste bits, including the centres that help chromosomes pull apart, and a few short ends that look almost identical. The old guide worked, but some turns were guesswork.
The new map-makers started with cells that kept things simple, like planning a city using one official street list instead of two slightly different ones. Then they did two surveys: one gave crisp notes but gave up in the lookalike areas; the other could follow a road for ages through repeats, but the notes were messier. Put together, they covered more ground.
They only snapped pieces together when the overlap matched exactly, like laying clear route strips on a table and joining them only when every turn lines up. Most streets became one clean line. In the copy-and-paste districts, the pieces tied into a knot, so they checked how often each block showed up, then used the longest drives to pick the real path through.
One district still fought back: the same building, over and over, with tiny changes. They stopped trying to name every single doorway in order. They grouped the building styles into a few types, worked out roughly how many of each type there were from the long drives, and filled in the district as solid blocks. The map gained a complete outline, even if some exact ordering stayed uncertain.
When the new city map came back from the printers, the torn strips were gone everywhere except one route I couldn’t draw from my chosen depot sheet. Lots of small wrong turns on the old map were fixed too. With the fuller map, the sat-nav stopped snapping my bus onto the wrong parallel street. Same idea for human DNA: fewer readings land at the wrong address, so false alarms are less likely.