Dor flows everywhere, but is chaotic and useless in its raw state. However, it is prone to take on the characteristics of forms in its immediate area and be drawn to like forms. To use it you need to collect enough of it in one place and then focus it. Think of a Fibonacci spiral.
The AREA orients the Dor. No matter what the area looks like, the Dor has 'knowledge' of it. The CITY (or any structure that matches the area) collects it. The Dor is drawn to the smaller version of the AREA. The SHAPE drawn by the caster focuses it for use. Again, the Dor is drawn further by the ever smaller series of shapes that match the AREA.
The Chasm changed the AREA, ruining the orientation of the Dor. The CITY no longer collected because it no longer matched the AREA. The SHAPES no longer had anything to focus, and couldn't focus the local Dor, anyway. When the chasm was incorporated into the CITY, the CITY was able to collect the local Dor again. Modified SHAPES could then focus that collected Dor for use
I would assume GPS and GIS technology would allow modern people to focus all of the Dor from extremely vast areas of the planet. Structures that match continents and shapes that mirror those structures would allow God-like powers.