A common problem with many hacks that have edited the Town Map is that when checking the Town Map, you don't always appear at the right position. This is because the game looks at a table that determines the width and height of each map name when checking the Town Map.
The table is located at
0x3F2178. The format is very simple:
[WW] 00 [HH] 00
WW = Width
HH = Height
I've wrote out the offsets that will take you to the dimensions of the Kanto map locations:
3F2178 = PALLET TOWN
3F217C = VIRIDIAN CITY
3F2180 = PEWTER CITY
3F2184 = CERULEAN CITY
3F2188 = LAVENDER TOWN
3F218C = VERMILION CITY
3F2190 = CELADON CITY
3F2194 = FUCHSIA CITY
3F2198 = CINNABAR ISLAND
3F219C = INDIGO PLATEAU
3F21A0 = SAFFRON CITY
3F21A4 = ROUTE 4
3F21A8 = ROUTE 10
3F21AC = ROUTE 1
3F21B0 = ROUTE 2
3F21B4 = ROUTE 3
3F21B8 = ROUTE 4
3F21BC = ROUTE 5
3F21C0 = ROUTE 6
3F21C4 = ROUTE 7
3F21C8 = ROUTE 8
3F21CC = ROUTE 9
3F21D0 = ROUTE 10
3F21D4 = ROUTE 11
3F21D8 = ROUTE 12
3F21DC = ROUTE 13
3F21E0 = ROUTE 14
3F21E4 = ROUTE 15
3F21E8 = ROUTE 16
3F21EC = ROUTE 17
3F21F0 = ROUTE 18
3F21F4 = ROUTE 19
3F21F8 = ROUTE 20
3F21FC = ROUTE 21
3F2200 = ROUTE 22
3F2204 = ROUTE 23
3F2208 = ROUTE 24
3F220C = ROUTE 25
3F2210 = VIRIDIAN FOREST
3F2214 = MT. MOON
3F2218 = S.S. ANNE
3F221C = UNDERGROUND PATH
3F2220 = UNDERGROUND PATH
3F2224 = DIGLETT'S CAVE
3F2228 = VICTORY ROAD
3F222C = ROCKET HIDEOUT
3F2230 = SILPH CO.
3F2234 = POKéMON MANSION
3F2238 = SAFARI ZONE
3F223C = POKéMON LEAGUE
3F2240 = ROCK TUNNEL
3F2244 = SEAFOAM ISLANDS
3F2248 = POKéMON TOWER
3F224C = CERULEAN CAVE
3F2250 = POWER PLANT
(Sevii Islands continue on right after, I only wrote Kanto offsets because I'm lazy)
Now to demonstrate what I mean, let's say you're in Pallet Town.
At 0x3F2178, the offset for Pallet Town's dimensions (as well as the start of the whole table), we see the bytes 01 00 01 00. The first 01 simply means that on the Town Map, Pallet Town is only 01 tile high, and the second 01 simply means that on the Town Map, Pallet Town is only 01 tile wide.
Because of that, no matter where you are in Pallet Town, on the Town Map, you'll be limited to those dimensions:
Now lets change Pallet Town's Town Map width to 03. Simply change the byte at 0x3F2178 to 03. Now let's walk all the way to the right side of Pallet Town.
So we changed Pallet Town's Town Map width to 03, let's check the Town Map:

As you can see, it affects our visual position on the Town Map. This is because we altered Pallet Town's Town Map width to 03.
If we go to the middle of Pallet Town, then we get this:
And all the way to the left:
The same applies to height. This is how your position is controlled on the Town Map, as each Map name as a width and height associated with it.