The bulk of Lost Sectors are scattered around EDZ. Myself and a few other artists worked across all of them to make significant extra chunks of content for players to explore outside of the main story. Most of these spaces are entirely optional, but players get the opportunity to get some nice loot and lore if they so choose to explore. Each space was built to encapsulate a certain theme.
Many thanks must be given to Sam Rucks and Matt Turner who did a lot of work on these before I was brought in.