Ikseon-Dong 166 is one of the traditional urban resident area developed during 1930’s. The purpose of this research is to analyze the structural relationship between a conventional housing unit plans and modern block plans based on orthogonal geometry. To fully explore the selling point of the new urban development, the planner or real estate developer in private sector did not abandon or compromise the conventional house layouts, consists of single layer of rooms keeping the main room facing south. This study concludes the following factors connecting the urban and architectural plans. Oblong block plans following east-west direction did not allow the southern exposure of courtyard and main room, which was the absolute requirement for traditional house units, the longer side of block plan followed north-south direction as a result. Considering the possibility of rent, having entrance at the east or west side of individual site enables two separate household maintain their spatial privacy. In addition to the factors mentioned above, when the blocks are to be divided into individual addresses, north-south oblong block plans maintained the length to face the front road minimum while the southern exposure maximized. These factors explains why the private developers maintained their blocks elongated to north-south direction when the block plans laied out by public sectors which did not care that much of southern exposure show random orientation in the view point of solar exposure.