A　single　layer　of　LaAlO3　with　a　nominal　thickness　of　one　unit　cell,　which　is　sandwiched　between　a　SrTiO3　substrate　and　a　SrTiO3　capping　layer,　is　quantitatively　investigated　by　high-resolution　transmission　electron　microscopy.　By　the　use　of　an　aberration-corrected　electron　microscope　and　by　employing　sophisticated　numerical　image　simulation　procedures,　significant　progress　is　made　in　two　aspects.　First,　the　structural　as　well　as　the　chemical　features　of　the　interface　are　determined　simultaneously　on　an　atomic　scale　from　the　same　specimen　area.　Second,　the　evaluation　of　the　structural　and　chemical　data　is　carried　out　in　a　fully　quantitative　way　on　the　basis　of　the　absolute　image　contrast,　which　has　not　been　achieved　so　far　in　materials　science　investigations　using　high-resolution　electron　microscopy.　Considering　the　strong　influence　of　even　subtle　structural　details　on　the　electronic　properties　of　interfaces　in　oxide　materials,　a　fully　quantitative　interface　analysis,　which　makes　positional　data　available　with　picometer　precision　together　with　the　related　chemical　information,　can　contribute　to　a　better　understanding　of　the　functionality　of　such　interfaces.