The A(2)BX(4) family of compounds manifest a wide range of physical properties, including transparent conductivity, ferromagnetism, and superconductivity. A 98% successful diagrammatic separation of the 44 different crystal structures of 688 oxide A(2)BX(4) compounds (96% for 266 oxide-only) is described by plotting the total radius of the A atom R-A versus the radius of the B atom R-B for many A(2)BX(4) compounds of known structure types and seeking heuristically simple, straight boundaries in the R-A versus R-B plane that best separate the domains of different structure types. The radii are sums R-A = R-s(A) R-p(A) of the quantum-mechanically calculated "orbital radii" R-s(R-p), rather than empirical radii or phenomenological electronegativity scales. These success rates using first-principles orbital radii uniformly exceed the success rates using classic radii. Such maps afford a quick guess of the crystal structure of a yet unmade A(2)BX(4) compound by placing its atomic orbital radii on such maps and reading off its structure type.