A portable electronic system (80, 302) comprising: a sensor configured to capture three-dimensional information about objects in a physical world; a local memory; a transceiver configured for communication over a computer network with remote memory; a processor (3812, 3822) configured to execute computer executable instructions to provide a 3D representation of a portion of the physical world based at least in part on the 3D information about the objects in the physical world, wherein: the 3D representation of the portion of the physical world comprises a plurality of blocks, the plurality of blocks having versions, each version having values representing objects in a region of portion of the physical world at a point in time; and the computer executable instructions comprise instructions for: identifying a subset of the plurality of blocks corresponding to the portion of the physical world; and selecting versions of blocks representing the subset of blocks by (i) accessing previously stored versions of blocks in the local memory or (ii) accessing previously stored versions of blocks in the remote memory and/or (iii) generating new versions of blocks based at least in part on the 3D information about the objects in the physical world. a sensor configured to capture three-dimensional information about objects in a physical world; a local memory; a transceiver configured for communication over a computer network with remote memory; a processor (3812, 3822) configured to execute computer executable instructions to provide a 3D representation of a portion of the physical world based at least in part on the 3D information about the objects in the physical world, wherein: the 3D representation of the portion of the physical world comprises a plurality of blocks, the plurality of blocks having versions, each version having values representing objects in a region of portion of the physical world at a point in time; and the computer executable instructions comprise instructions for: identifying a subset of the plurality of blocks corresponding to the portion of the physical world; and selecting versions of blocks representing the subset of blocks by (i) accessing previously stored versions of blocks in the local memory or (ii) accessing previously stored versions of blocks in the remote memory and/or (iii) generating new versions of blocks based at least in part on the 3D information about the objects in the physical world. the 3D representation of the portion of the physical world comprises a plurality of blocks, the plurality of blocks having versions, each version having values representing objects in a region of portion of the physical world at a point in time; and the computer executable instructions comprise instructions for: identifying a subset of the plurality of blocks corresponding to the portion of the physical world; and selecting versions of blocks representing the subset of blocks by (i) accessing previously stored versions of blocks in the local memory or (ii) accessing previously stored versions of blocks in the remote memory and/or (iii) generating new versions of blocks based at least in part on the 3D information about the objects in the physical world. identifying a subset of the plurality of blocks corresponding to the portion of the physical world; and selecting versions of blocks representing the subset of blocks by (i) accessing previously stored versions of blocks in the local memory or (ii) accessing previously stored versions of blocks in the remote memory and/or (iii) generating new versions of blocks based at least in part on the 3D information about the objects in the physical world.