The continuous displacement field within elastically relaxed GaInAs islands was calculated from digitized HREM images of {110} cross sections of In0.35Ga0.65As layers grown on GaAs by molecular beam epitaxy. Experimental maps of the deformations parallel to the interface (εx) and along the growth direction (εz) were drawn and compared with the ones calculated via the finite element method. It was found that εx exp was systematically higher than εx calc and the significant maximum observed for εz exp within the island could not be found for εz calc. These discrepancies were attributed to a variation of the chemical composition in the island. The maps showing the indium concentration gradient drawn from HREM and FE calculations were compared to quantitative profiles for indium concentration obtained by nanometric X-ray microanalysis in TEM. The measured gradient within the island backs our assumption.