The basic monocentric city model implies a decreasing relationship between distance to the Central Business District and outcome variables such as population density, housing prices, land rent, and income. Implicitly, the monocentric model implies directional homogeneity, that is, the distance effect does not depend on the direction in which it is being measured. Only a few works have analyzed the problem of directional heterogeneity. A new conditional parametric approach is introduced to deal with the issue. We study how this approach performs under different spatial patterns comparing with several other methods. An application to the spatial distribution of wage income in the municipality of Madrid is carried out to illustrate the main characteristics of the method and to show the comparative advantages.