Before the invention of the GPS, city planners wrote an algorithm to help citizens locate any point within the grid. Assuming you know the building number and either a North-South street name OR a East-West street name, you will be able to triangulate to your desired location.
For example, if you know that the building is at #1165 Third Avenue (running North-South), using the algorithm and its associated table of Keys, you can decode that the address is at 68th street. The resulting X-Y coordinates on the grid will get you to your destination.
Before we reveal the algorithm, here are the basics:
Downtown means south of wherever you happen to be at the moment; uptown refers to all points north.
Approximately 20 north-south blocks equal a mile.
Approximately 10 east-west blocks equal a mile. The longest crosstown street
(14th Street) is 2.3 miles.
Traffic is one-way going east on even-numbered streets.
Traffic is one-way going west on odd-numbered streets.
(However the major east-west streets are two-way and some smaller streets don't follow the rule).
Sixth Avenue is actually named Avenue of the Americas, but New Yorkers refer to it as Sixth Avenue, regardless of what the street signs read.
Fourth Avenue becomes Park Avenue South
above 14th Street.
OK, we are ready for the heavy stuff.
First, determine if you are looking to find the cross street intersecting with a North-South avenue or intersecting with a East-West street. You will use a different algorithm for each.
Here is the process if you are looking for the intersecting East-West street:
1) Cancel the rightmost digit of the house address.
2) Divide the remainder by 2.
3) Add or Subtract from the result a Key number from TABLE A below:
TABLE A
Avenues A, B, C, D, First, and Second: ADD 3.
Third Ave: ADD 10
Fourth Ave: ADD 8
Ave of the Americas: SUBTRACT 12
Eighth Ave: ADD 9
Ninth and Tenth Ave: ADD 13
Eleventh Ave: ADD 15
Amsterdam and Columbus Ave: ADD 59
Lexington Ave: ADD 22
Madison Ave: ADD 27
Park Ave: ADD 34
West End: ADD 59
Central Park West: ADD 60
Some avenues are slightly more complicated. They have more Key numbers because of their length.
Seventh Ave:
If the building number is in the range between 1-1800, ADD 12
If it is in the range between 1801 and up, ADD 20
Fifth Ave:
1-200, ADD 13
201-400, ADD 16
401-600, ADD 18
601-775, ADD 20
776-1286, SUBTRACT 18.
Riverdale Drive:
1-567, ADD 73
568-up, ADD 78
Broadway:
1-753, below 8th street does not adhere to the algorithm
754-858, SUBTRACT 29
858-958, SUBTRACT 25
1000-up, SUBTRACT 31
Great! Your doing fine. A few more details, and you will be ready for your NYC Taxi-drivers exam.
Here is the process if you are looking for the intersecting North-South avenue:
1) Determine if you are on the East Side or the West Side.
2a) If you are are the East Side, cross-reference the building number from TABLE B below:
TABLE B
1-100 Fifth Ave.
101-200 Park Ave.
201-300 Third Ave.
301-400 Second Ave.
401-500 First Ave.
501-600 York Ave. or Ave A
601-up Ave. B
2b) If you are are the West Side, cross-reference the building number from TABLE C below:
TABLE C
1-100 Fifth Ave.
101-200 Ave. of the Americas (6th Ave)
201-300 Seventh Ave.
301-400 Eighth Ave.
401-500 Ninth Ave.
501-600 Tenth Ave.
601-up Eleventh Ave.
You can see from the addressing scheme in Tables B and C that a street address MUST include the EAST or WEST designation, since there are likely duplicate numbers in the range.
Buy the way, there is a freeware PalmPilot program called X-Man that will do this for you, and a web page as well: http://www.ny.com/locator/
I'm sure Apple has an iPhone "App for That." Lots of New Yorkers seem to have iPhones.
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And remember, there are always exceptions to the rule.
