A unified operation mode of synthetic aperture imaging ladar (SAIL) with its linear moving and the footprint scanning is proposed. Moreover, we define a kind of two-dimensional (2-D) data collection equation based on the developed point target ladar equation, which is a complete mathematical description of data acquisition for 2-D SAIL imaging. The unified mode can be decomposed into strip-map mode, spotlight mode, sliding spotlight mode and beam scanning mode, and each correspondingly has a simplified 2-D data collection equation. The beam scanning mode with only the footprint scanning is a new mode, and has special applications.