Rossmo's formula is a geographic profiling formula to predict where a serial criminal lives. It relies upon the tendency of criminals to not commit crimes near places where they might be recognized, but also to not travel excessively long distances. The formula was developed and patented in 1996 by criminologist Kim Rossmo and integrated into a specialized crime analysis software product called Rigel. The Rigel product is developed by the software company Environmental Criminology Research Inc. (ECRI), which Rossmo co-founded.
Formula Imagine a map with an overlaying grid of little squares named sectors. If this map is a raster image file on a computer, these sectors are pixels. A sector S i , j {\displaystyle S_{i,j}} is the square on row i and column j, located at coordinates ( X i , Y j ) {\displaystyle (X_{i},Y_{j})} . The following function gives the probability p i , j {\displaystyle p_{i,j}} of the position of the serial criminal residing within a specific sector (or point) ( X i , Y j ) {\displaystyle (X_{i},Y_{j})} :
p i , j = k ∑ n = 1 T [ ϕ i j ( | X i − x n | + | Y j − y n | ) f ⏟ 1 s t t e r m + ( 1 − ϕ i j ) ( B g − f ) ( 2 B − | X i − x n | − | Y j − y n | ) g ⏟ 2 n d t e r m ] , {\displaystyle p_{i,j}=k\sum _{n=1}^{T}\left[\underbrace {\frac {\phi _{ij}}{(|X_{i}-x_{n}|+|Y_{j}-y_{n}|)^{f}}} _{1^{\mathrm {st} }\mathrm {\;term} }+\underbrace {\frac {(1-\phi _{ij})(B^{g-f})}{(2B-|X_{i}-x_{n}|-|Y_{j}-y_{n}|)^{g}}} _{2^{\mathrm {nd} }\mathrm {\;term} }\right],}
where:
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