A method for reducing an effect of flare produced by a lithographic apparatus for imaging a design layout onto a substrate is described. A flare map in an exposure field of the lithographic apparatus is simulated by mathematically combining a density map of the design layout at the exposure field with a point spread function (PSF), wherein system-specific effects on the flare map may be incorporated in the simulation. Location-dependent flare corrections for the design layout are calculated by using the determined flare map, thereby reducing the effect of flare. Some of the system-specific effects included in the simulation are: a flare effect due to reflection from black border of a mask, a flare effect due to reflection from one or more reticle-masking blades defining an exposure slit, a flare effect due to overscan, a flare effect due reflections from a gas-lock sub-aperture of a dynamic gas lock (DGL) mechanism, and a flare effect due to contribution from neighboring exposure fields.