GEDTM30 (github.com/openlandmap/GEDTM30) is an open source global digital terrain model at 1 arc second. It is the first permissive license 1 arc-second terrain model of the world (under CC-BY license). Upon this model, we are presenting a framework to merge national, state-based or individual digital terrain models to improve GEDTM30 data quality locally. Due to a permissive license, GEDTM30 can be used as a base layer to create derived products. By merging local lidar DTMs with GEDTM30, it opens the gate to federation of data, sharing the common goods but keeps the best interests for individuals. This framework will be tested by GEDTM30 with lidar data from several countries (e.g. Romania, Italy, the Netherlands, Brazil, etc), and the land surface variables are included to assess the merged GEDTM30 quality. In the end, the code and framework will be open to serve any stakeholders to improve DTM quality of their area of interest and have freedom to decide for contribution.