The computerization of many phases in the production of the reconnaissance hydrogeological map series has encountered difficulties inherent to mapping in a complex coherent system. The National Topographic System, using Transverse Mercator projections, has polar coordinates. The Dominion Land Survey system is a synthesis of orthogonal and polar coordinate systems. The computer output device operates in an orthogonal system. If Dominion Land Survey coordinates are used as input and National Topographic Systems compatible maps are desired as output, mapping by computer must invoke a suitable translation program. The construction of such a program was undertaken by simplifying the coordinate system to the maximum extent consistent with keeping the resultant errors within set limits. The scale of 1:250 000 was used as a criterion for acceptability, as this scale is most commonly used in the reconnaissance map series. Simplicity of utilization was achieved by minimizing the parameters necessary to define the area to be plotted. These parameters were found necessary and additional ones useful. These parameters were: horizontal field in ranges, the vertical field in townships, the scale as a ratio, and two adjustment factors.