Progressive map maintenance at a mobile navigation unit

A system comprising a non-transitory computer-readable storage device comprising code that, when executed by a processing unit, causes the processing unit to perform operations comprising:

• receiving baseline map data from a remote map-data source;
• determining whether the baseline map data is sufficient for present mobile navigation-unit function, yielding a map-sufficiency determination;
• using, if the map-sufficiency determination is affirmative, the baseline map data for the present mobile navigation-unit function;
• and
• if the map-sufficiency determination is negative:
• predicting navigation-unit movement;
• obtaining, based on the navigation-unit movement predicted, supplemental map data;
• and
• using the baseline map data and the supplemental map data for the present mobile navigation-unit function.

A process, for implementation at a mobile navigation unit including a processing unit and a non-transitory computer-readable storage device having a nav-unit code, comprising:

• receiving, by the processing unit executing the nav-unit code, baseline map data from a remote map-data source;
• determining, by the processing unit executing the nav-unit code, whether the baseline map data is sufficient for present mobile navigation-unit function, yielding a map-sufficiency determination;
• using, by the processing unit, if the map-sufficiency determination is affirmative, the baseline map data for the present mobile navigation-unit function;
• and
• the processing unit, if the map-sufficiency determination is negative:
• predicting navigation-unit movement;
• obtaining, based on the navigation-unit movement predicted, supplemental map data;
• and
• using the baseline map data and the supplemental map data for the present mobile navigation-unit function.