A mathematical expression relating observed recombination fraction (q.v.) to map distance expressed in centiMorgans. Two common mapping functions are those developed by Haldane and Kosambi. In both functions, the relationship between recombination fraction and map distance is approximately linear for recombination fractions less than 10%; as recombination fraction increases above 10% (up to its maximum of 50%), map distance is increasingly greater than recombination fraction.