Simulated maps of source-averaged stellar microlensing optical depth τ. Top left: ground-based I-band view. Top right: ground-based K-band view. Bottom left: space-based H-band view. The colour bar scale is adjusted to the same range for comparison among bands. Bottom right: a real K_S-band mosaic of the inner Galaxy from the VVV survey. The image has been smoothed to render at approximately the same resolution as the microlensing maps and the intensity level has been squared, as the microlensing optical depth scales approximately as the square of the stellar density. VVV image credit: ESO/VVV Survey/D. Minniti, with acknowledgement to Ignacio Toledo and Martin Kornmesser.