1. A method for efficiently managing content of a landmark database in a visual simultaneous localization and mapping system, the method comprising: autonomously navigating a mobile device using one or more maps of the visual simultaneous localization and mapping system, and while autonomously navigating the mobile device, performing the following: creating new landmarks from images captured by a camera mounted on the mobile device; determining a density of the created landmarks in the one or more maps, wherein a landmark is associated with a pose of the mobile device that is determined when the landmark is created or updated when re-observed, wherein the pose corresponds to a position and orientation of the mobile device; and discontinuing the adding of new landmarks to the one or more maps at least partially in response to a determination that the density of landmarks is higher than a threshold such that memory can be freed for other tasks; wherein autonomously navigating, creating, determining and discontinuing are performed under the control of electronic hardware.