The immense amount of the mapping-phase Mars Global Surveyor (MGS) magnetic data allows us to derive a highly accurate magnetic map of Mars. The data acquired at nighttimes within the first ~3 years of the mapping phase are divided into two almost equal parts, and each part is expressed in spherical harmonics of degree up to 90. The two models are almost identical over harmonics of degree up to 62 but show appreciable differences over higher-degree harmonics, indicating that the higher-degree harmonic coefficients have appreciable noncrustal contribution. The most repeatable components of the two models are combined to produce an accurate 62-degree harmonic model of the magnetic field of the Martian crust. It is further demonstrated that the altitude of MGS is the major limiting factor of the resolution of the mapping-phase data. The small-scale features of the data, with wavelengths shorter than ~400 km, have significant contribution from noncrustal sources. They are not useful for delineating the details of the magnetic source bodies in the crust.