Transmission electron microscopy has been applied to study the ordering in size and shape of InAs quantum dots and in their lateral distribution. InAs islands were grown by MBE on GaAs substrates at different As-pressures and growth temperatures. Experiments with growth interupption support the theoretical predictions concerning equilibrium island size, shape and arrangement. The stability of the equilibrium dot arrays to changing of growth conditions was studied by varying the deposition temperature, arsenic pressure or growth interruption time. Significant deviation from the optimal As-pressure towards both the lower and higher values was shown to supress the formation of InAs dots resulting either in mesoscopic InAs clusters or 2D corrugated islands. Energy benefit due to the strain relaxation at island edges explains the experimental results better than kinetic consideration.