In the plugin controls, select your "Tiles" composition as the source for the pattern.
If you have a map of a city, you can use Pixmap to overlay a grid of "buildings" that grow or change color based on the brightness of a heat map layer underneath. Performance Tips Pixmap Plugin After Effects
The Pixmap plugin for After Effects is more than just a stylization tool; it’s a powerhouse for anyone looking to push the boundaries of grid-based design. By treating every pixel as a container for more complex imagery, it allows you to create intricate, high-detail visuals with a fraction of the manual effort. In the plugin controls, select your "Tiles" composition