Chapter three talks about the curvature maps or corneal power maps. It includes an explanation of the principle of spherical refractive surface power equation, methods of measurements, and patterns of corneal curvature. There are two methods of measurements, the sagital or axial method, and the tangential or local method. The former depends on a reference axis, while the latter depends on local circles. There are three reference axes, the visual axis, the anatomical axis, and the videokeratoscope normal or the VK normal. Normal patterns of corneal curvature are described including the symmetric bowtie representing with-the-rule astigmatism, against-the-rule astigmatism or oblique astigmatism. Abnormal patterns that characterize irregularity are also described, including the round, oval, superior steep, inferior steep, irregular, symmetric bowtie with and without skewed radial axes or what is called non-orthogonal astigmatism, asymmetric bowtie with and without skewed radial axes, asymmetric bowtie inferior steep, asymmetric bowtie superior steep, the smiling face, junctional, and finally the vortex pattern. At the end of this chapter, clinical differences between sagital and tangential curvature maps are mentioned.