The study deals with nonferrous two-dimensional arrays of line currents, creating magnetic fields suitable for guiding or focusing particle beams. Methods have been found to reduce stray fields to the level of one part per thousand of the useful magnetic field and reach precision of the useful field to the level of 100 ppm. Complex potential theory is used throughout. In particular, the method is applied to the design of a dc superconducting dipole septum magnet, which can be used for inflection of a particle beam into a storage ring, leading to the concept of the truncated double cosine theta septum magnet. The space required for the septum can be made small, so that the device may compete with similar room temperature puulsed septum magnets. The Lorentz forces have been evaluated, including those which occur when the device is immersed in the field of another magnet. Selected combinations of multipoles are considered, showing novel ways to reduce stray fields.