Route density is how close together a day's jobs are. Ten yards on three adjacent streets is a dense route; ten yards scattered across the county is a sparse one — same revenue on paper, wildly different profit, because the sparse route spends its margin on windshield time.
Density compounds. A dense pocket means less drive time per stop, which means more stops per day, which makes it easier to quote competitively in that pocket, which wins more neighbors, which increases density further. This is why established operators can profitably charge less than a newcomer in their home neighborhoods, and why 'we service your street on Thursdays' is such an effective sales line — it's true, and it's cheaper to deliver.
Building density deliberately. Cluster service days by area instead of by customer preference where you can. Price distant one-offs with their true drive cost (see job costing) or decline them. Ask happy customers about neighbors — the referral next door is worth more than a bigger yard across town. And when two customers sit on the same street on different days, consolidating them is a raise nobody has to pay for.
Density and optimization are partners, not the same thing. Route optimization finds the best order through the stops you have; density determines how good that best order can possibly be. Software can't shorten the drive between two towns — only your customer-acquisition choices can.
In Grassr, the route map and per-crew routing make the density picture visible day by day, and the scheduling flow makes area-based service days the default rather than a discipline you maintain by hand.