There exists a business in which storage-space is rented.
For decades they tended to occupy a significant chunk of
landscape, to allow easy ground-level access to each
storage unit (various sizes available) of the facility.
Recently I've seen some multi-storey storage facilities
getting built,
so I'm guessing they incorporate very
powerful elevator systems, for moving large amounts of
stuff easily between ground level and the level of some
particular storage unit.

Even the multi-storey facilities still occupy more
landscape
than necessary, however, and this Idea is about a way to
shrink them significantly (or to put a lot more units into
the same space as before). It depends partly upon a lot
of
statistical data about how many of the storage units in a
typical facility are ever accessed at the same time....

First, we need to select a size for a storage unit. A
common size is about 3 meters x 3 meters of floor area.
For the purposes of this Idea, we shall offer 3 sizes, a
2x2-
meter space, a 3x3-meter space, and a 4x4-meter space.
All the units are the same height --let's go with 3 meters.
This facility is 3 storeys high, with all the storage units
on
each floor being the same size.

Each storage unit is literally a box, strongly built. There
are doors on all four of its walls, and each box is move-
able. It has a bunch of caster wheels on the bottom, and
an RFID chip on top, along with means of being grabbed
(by
ceiling-mounted machinery) and moved.

Now see the link, for a classic puzzle/game. Imagine all
the squares EXCEPT ONE occupied by a storage-unit box,
and an aisle completely surrounding the overall square.

Remember what I said earlier, about how many of the
units
are ever simultaneously accessed? A 5x5 array of move-
able storage-unit boxes has 24 total in that array, with 8
on the inside and 16 on the outside. If as many as 2/3 of
all the units are ever accessed simultaneously, this array
would be fine.

However, if all the units are simultaneously ever
accessed
to a lesser extent, then a 6x6 array (or more) might be
preferred. it will contain 35 move-able storage-unit
boxes,
of which 15 would be on the inside and 20 on the outside
(4/7 of them accessible at once). A 7x7 array would hold
48 move-able units, with 24 on the inside and 24 on the
outside (50% accessible simultaneously). An 8x8 array
would hold 63 units, with 35 on the inside and 28 on the
outside (4/9 accessible simultaneously). Historical usage
statistics are extremely critical to this Idea!

Note that where-ever one's particular rented storage unit
might be, the "puzzle" consists of finding the shortest
path
for moving that unit to the outside edge of the array.
The
renter can be told where, along the outside aisle, to go
to
await the arrival of the storage box. I suspect the
corner-
locations will always be prime destinations (never want
to
shift any box getting accessed!!). I'm sure computers can
solve that simple a puzzle with ease.

(Technically, there will probably always be one less than
the maximum of simultaneously-accessible outer boxes,
due to the need to be able to shift at least two of them,
to
move a desired box to the outside. If the array had two
holes in it instead of one, though, then only shifting a
corner box becomes problematic to its neighbors.
Perhaps the corner-boxes should be permanently fixed in
place, and never moved? They would only need 2 doors
each, but renters could be charged more, for the
convenience of always knowing where to go to access
their stuff.)

When someone closes the door to the storage unit, the
system can then know that the renter is done, and that
space along the surrounding aisle is now available to a
different renter.
The purpose of the RFID chips is to make sure the units
can
be re-identified if a complete power failure happens to
cause location-data to be lost.