Downtown division is Central dispatch. Any 1AXX unit (I don't know the exact beat) would be near or in downtown. They dispatch 2 district on the same channel which is north of downtown out to the loop (2AXX Units). Each division has it's own set of districts (NW division is districts 4 and 5 which is dispatched on Northwest channel, but also 18 district, Midwest Division, is dispatched on NW too, North division is 3 and 6, North Belt is 22 all dispatched on the North channel, etc..). Special Ops units work all over the city (any special division is on this channel from DWI, Accident investigators, etc...). It's kind of confusing for anyone who hasn't monitored HPD before.
So with that being said a single dispatch channel can dispatch multiple divisions. The only common denominator between the units and each dispatch channel is the Letter in the middle of the unit number so for instance even though they could be different divisions 1A10 and 2A10 both have the A in the middle (which would be the central dispatch channel). 5F30 and 18F30 are nowhere near each other geographically, nor the same division, but since they are dispatched on the same channel (Northwest) the F is common.
I hope that's about as clear as mud...
Here is a link to HPD's official district map: https://www.houstontx.gov/police/pdfs/hpd_beat_map.pdf You will notice that 1A10's beat is a different color because it is now patrolled by Special Ops units and you will never hear a unit such as 1Adam10, 1 Adam12 on the air
