In Flight Simulator, when the object system is used to design scenery, the object coordinate system is used. The object coordinate system is based on the X, Y, Z concept of design space. The SCALE command is used to specify a latitude, longitude, altitude, and scale factor in the world coordinate system. The rectilinear, 3-D X,Y,Z coordinate system is set up with its center, X=Y=Z=0, at the specified latitude, longitude, and altitude. The Z axis aligns with true north (parallel to lines of longitude), the X axis aligns with east (parallel to lines of latitude), and the Y axis aligns with altitude. You can define points, lines, and polygons within the X,Y,Z design space.
The X,Y, and Z axis each have a range of +/-32767 (16-bit linear design space). The size that each unit along the axes represents depends on the scale factor. The scale factor can range from less than 1 mm per unit to 32768 M per unit.
In the object coordinate system, each SCALE command is setting up a unique coordinate system; each coordinate system has not only a different design scale, but also a different rotational orientation to other SCALE commands because it is located in a different position on the surface of a sphere (the earth).
The object design system creates some interesting design problems that are not unlike those in the real world. For example, a 1-mile square section of land in the northern hemisphere encompasses more longitude at its northern edge because this edge is further north on the sphere. Conversely, a "square" piece of land that has its east and west borders precisely aligned with lines of longitude and its north and south borders aligned with lines of latitude isn’t really square because its north edge is shorter than its south edge. When aligning many square pieces on the earth’s surface, the result is either some pieces that aren’t square or small gaps between some pieces.