Some embodiments of the invention are directed to techniques for electrochemically fabricating multi-layer three-dimensional structures where selective patterning of at least one or more layers occurs via a mask which is formed using data representing cross-sections of the three-dimensional structure which has been modified to place it in a polygonal form which defines only regions of positive area. The regions of positive area are regions where structural material is to be located or regions where structural material is not to be located depending on whether the mask will be used, for example, in selectively depositing a structural material or a sacrificial material. The modified data may take the form of adjacent or slightly overlapped relative narrow rectangular structures where the width of the structures is related to a desired formation resolution. The spacing between centers of adjacent rectangles may be uniform or may be a variable. The data modification may also include the formation of duplicate copies of an original structure, scaled copies, mirrored copies, rotated copies, complementary copies, and the like.