Maroni divisors on Hurwitz spaces

The moduli spaces H_{d,g} of covers of genus g and degree d of the projective line are known as Hurwitz spaces. We will discuss the Maroni stratification on such Hurwitz spaces. This stratification has a stratum that is a divisor only if d − 1 divides g and we will give an approximation of the class of this divisor in the compactified Hurwitz space. This is joint work with Gerard van der Geer.