SQL Number - Row_Number() - Allow Repeating Row Number

I'm using SQL Server 2008. I have this data returned in a query that looks pretty much like this ordered by Day and ManualOrder...

ID   Day  ManualOrder  Lat     Lon    
1    Mon  0            36.55   36.55  
5    Mon  1            55.55   54.44  
3    Mon  2            44.33   44.30  
10   Mon  3            36.55   36.55  
11   Mon  4            36.55   36.55  
6    Mon  5            20.22   22.11  
9    Mon  6            55.55   54.44  
10   Mon  7            88.99   11.22  
77   Sun  0            23.33   11.11  
77   Sun  1            23.33   11.11  

What I'm trying to do is get this data ordered by Day, then ManualOrder...but I'd like a row counter (let's call it MapPinNumber). The catch is that I'd like this row counter to be repeated once it encounters the same Lat/Lon for the same day again. Then it can continue on with the next row counter for the next row if it's a different lat/lon. We MUST maintain Day, ManualOrder ordering in the final result.

I'll be plotting these on a map, and this number should represent the pin number I'll be plotting in ManualOrder order. This data represents a driver's route and he may go to the same lat/lon multiple times during the day in his schedule. For example he drives to Walmart, then CVS, then back to Walmart again, then to Walgreens. The MapPinNumber column I need should be 1, 2, 1, 3. Since he goes to Walmart multiple times on Monday but it was the first place he drives too, it's always Pin #1 on the map.

Here's what I need my result to be for the MapPinNumber column I need to calculate. I've tried everything I can think of with ROW_NUMBER and RANK, and going insane! I'm trying to avoid using an ugly CURSOR.

ID   Day  ManualOrder  Lat     Lon     MapPinNumber
1    Mon  0            36.55   36.55   1
5    Mon  1            55.55   54.44   2
3    Mon  2            44.33   44.30   3
10   Mon  3            36.55   36.55   1
11   Mon  4            36.55   36.55   1
6    Mon  5            20.22   22.11   4
9    Mon  6            55.55   54.44   2
10   Mon  7            88.99   11.22   5
77   Sun  0            23.33   11.11   1
77   Sun  1            23.33   11.11   1