How is the national electoral register created?

EU Election Observation Mission: Uganda, Presidential, Parliamentary and Local Council Elections [Final Report], accessed 4 November 2018

“The newly introduced voter registration system aimed to improve inclusiveness and accuracy of the voter register (VR). The EC compiled a new voter register for the 2016 general elections by extracting data on voting age citizens from the National Identification Register (NIR), changing the voter registration system from an active to a passive one.”