Fastest way to identify area from 2D coordinates

Question

I have the following code:

def findRegion(lat,lon):
    '''Gets a lat between -90,90 and a lon between -180,180 and returns a character'''
    if lat >= 50:
        y='ABCD'
    elif lat >= 0:
        y='EFGH'
    elif lat <= -50:
        y='MNOP'
    else:
        y='IJKL'

    if lon <= -90:
        x='AEIM'
    elif lon <= 0:
        x='BFJN'
    elif lon <= 90:
        x='CGKO'
    else:
        x='DHLP'

    for c in y:
        if c in x:
            return c

This function gets two coordinates and returns one of the 16 sector codes shown here . The code works perfectly, but it will get called lots of times, so I'm looking for the fastest possible solution. Any suggestions are much appreciated.

Answer 1

This should speed the process by using the x and y to find the region in a one dimensional string. May actually be slower due to the use of clamp.

clamp = lambda n, minimum, maximum: max(min(maximum, n), minimum)

def a(lat, lon):
    ## get lat, lon sections
    sec_lat = clamp((lat+90)/45,0,3)
    sec_lon = clamp((lon+180)/90,0,3)

    ## convert two values into a 1 dimensional list value
    sec = sec_lat*4 + sec_lon

    return "MNOPIJKLEFGHABCD"[sec]

Answer 2

This would improve the speed a little bit by skipping the double for(which is really marginal since there is only 4 iterations per loop so a worst case of 16 character comparisons) at the end of the function. Although, I would think the major improvement is in the readability which is often more important.

def findRegion(lat, lon):
    regions = ( ('A', 'B', 'C', 'D'), ('E', 'F', 'G', 'H'), ('I', 'J', 'K', 'L'), ('M', 'N', 'O', 'P'))

    lat_index = 0;
    if lat >= 50:
        lat_index = 0
    elif lat >= 0:
        lat_index = 1
    elif lat <= -50:
        lat_index = 2
    else:
        lat_index = 3

    lon_index = 0
    if lon <= -90:
        lon_index = 0
    elif lon <= 0:
        lon_index = 1
    elif lon_index <= 90:
        lon_index = 2
    else:
        lon_index = 3

    return regions[lat_index][lon_index]

print findRegion(-45, 50)