The shape of a street map is a historical document. Each pattern in it was produced by someone with the power to lay out land, and the pattern survives long after they do.
Irregular cores grew without a planner
Winding, narrow streets that meet at odd angles indicate growth by accumulation. Paths formed between buildings as people walked, and building followed the paths.
Property boundaries in such districts are ancient and hard to alter, which is why they resist redevelopment. Assembling enough adjacent plots to build anything large is impractical.
These cores are usually the oldest inhabited part of a city and often the most valuable. Their form is protected precisely because it cannot be recreated.
Straight grids indicate an act of authority
A regular grid means somebody surveyed land and imposed a plan before building began. Colonial administrations, military engineers and land companies all produced them.
Grids make land easy to divide, sell and tax, which is usually the actual motivation. Legibility for the administration comes before convenience for residents.
Where a grid meets an older core at an awkward angle, the join marks the moment of imposition. That seam is often the most confusing part of a city to walk.
Radial avenues were cut through existing fabric
Broad diagonal boulevards slicing across an older pattern were driven through built-up areas at great cost. They usually date from the era of grand urban rebuilding.
The stated purposes were sanitation, traffic and monumental views. Control of crowds and rapid movement of troops featured in the reasoning as well.
The buildings lining them are uniform in height and style because they were built at once to a single code. That uniformity is how the cut is recognised.
Walls leave a signature after removal
A ring road, a curved boulevard or a chain of parks encircling a centre almost always marks a demolished city wall. The land became public when the fortification lost its purpose.
Gates survive in place names even where the structures are gone. A street named for a gate marks where the boundary was and where tolls were once collected.
Outside that ring, the pattern usually changes abruptly. Suburbs beyond a wall developed under different rules and at a different density.
Reading a map before walking
Ten minutes with a street map identifies the sequence of a city's growth without any reading. The oldest quarter, the planned extension and the modern periphery are all visible in the geometry.
That sequence predicts where things are. Markets and religious buildings cluster in the old core, civic institutions on the planned avenues, and industry beyond the former walls.
It also predicts where walking is pleasant. Pedestrian scale survives where the plan predates vehicles, and disappears where the plan anticipated them.