Hi Cas. I think of the most commonnmistakes when mapping Hanoi is to look at satellite imagery and assume that the is no alignment between the building. I remember I deleted it because it looks like mess. The facades should be aligned together in a line and looks more like a solid block with straight edges and curves. You can look at this area as a good example: https://www.openstreetmap.org/changeset/151147174#map=17/21.01488/105.85045