EMS Vehicles
Vehicle Numbering is as follows (outside of Toronto):
First digit refers to the region. Regions 1 to 6, 1 in soutwestern Ontario, 6 in the north-west etc.
Second digit can mean a variety of things. 0 or 1 refers to a single stretcher vehicle, 2 is for a 2 stretcher unit, 3 is a non-transport response unit or supervisor vehicle, 4 is a support vehicle, 5 a regional spare ambulance
The 3rd and 4th digits are assigned sequencially.
for example, 6012 is a North-west region, single vehicle Ambulance, 3222 is a central region (actually York EMS) 2 stretcher ambulance, 5312 a response vehicle in Sudbury
In Toronto:
The number you see on the vehicle only partially relates to what you'll hear on the air. Generally, of the 3 digit numbers on the vehicle, beginnning with 9 are BLS and 8 are ALS or special ops (Tactical, PSU, CCTU etc).
On the air, for BLS units, station number followed by last 2 digits of the vehicle number. so vehicle 975 operating out of 43 station would be 4375.
ALS is the same, but add 4 to the first digit, so the same unit as ALS would be 8375.
Stations are numbered by quadrant with the dividing lines as roughly Yonge St and Eglinton Avenue. North-west is 1, North-east 2, South-west 3, South-east 4.
Any current Toronto medics feel free to correct any errors, I have friends who work for Toronto EMS but haven't worked land EMS there since I was a student.
As for Air Unit numbers:
prefix of 7 is the region number for air, and the other numbers were just assigned sequencially and refer the base. Only dedicated bases have numbers all beginnning 779, charter flight numbers are only used as flight numbers just like any other airline. The dedicated air operators use the 779x numbers as flight numbers, and they drop the first 7 such as "Voyageur 796" or "Canadian 798",. Only exception is Toronto where they regularly operate 2 aircraft. The primary aircraft to Air-traffic control will be "Canadian 799" and the Secondary "Canadian 790". BUt as far as CACCs are concerned the aircraft are both 7799 but differenciated by the last letter of their registration, so C-GIMZ would be 799Z and C-FABH, 799H.
Hope that helps.