The Coordinate System
The canvas pixel grid, the top-left origin, and why y counts downward.
Before a single mark appears, there is the grid. Every pixel on the canvas holds an address — a pair of numbers descended from René Descartes, whose seventeenth-century insight that geometry could be written as algebra still underwrites the screen. But the digital canvas inverts the schoolbook plane: the origin sits at the top-left and y increases downward, a convention inherited from raster scanning, where electron beams swept CRT screens left to right, top to bottom. To address space numerically is also to make it instructable, as in Sol LeWitt's wall drawings, where a coordinate is a command. Casey Reas and Ben Fry built Processing on exactly this premise — location is the first vocabulary of visual code.