Shadow mapping is a commonly used technique for generating hard shadows in computer graphics, but the generated shadow boundaries often suffer from aliasing due to the discrete nature of the shadow map. In this paper we introduce a new hardware accelerated algorithm which is capable of adjusting shadow map sampling rates inside a shadow map of constant size. This is achieved by tiling the light view and changing the sampling quality according to a heuristical analysis. The implementation is straightforward on current consumer level graphics hardware and the algorithm can therefore be included into existing applications. In our test scenarios the cost of the improved image quality was moderate, making this method a viable option for increasing the quality of hard shadows.