The numbers outside the grid show how many buildings can be seen when looking towards the grid. So, for example, the 2 at the beginning of the fifth row means that the following combinations could be found in that row:
51874362
64873125
The small figures in the shaded rectangles show the total of the numbers in that rectangle.
"The shaded rectangles are similar to those found in "Killer Sudoku".
7 | |||||||||||
21 | 12 | 6 | 15 | ||||||||
15 | 3 | 10 | |||||||||
21 | 13 | 6 | 7 | ||||||||
6 | 10 | 11 | 11 | ||||||||
2 | 5 | ||||||||||
19 | 1 | ||||||||||
8 | 15 | 5 | 4 | ||||||||
10 | 12 | ||||||||||