1. A method, implemented at a computer system that includes one or more processors and memory, the method comprising: instantiating a data stream object that is associated with a data stream, the data stream itself not being entirely within the memory of the computing system although the data stream object is within the memory of the computing system; passing a request for a portion of the data stream to the data stream object, the request requesting member elements of the data stream that correspond to a particular visual zoom level; the data stream object identifying the member elements of the data stream that correspond to the particular visual zoom level; the data stream object accessing one or more portions of the data stream that correspond to the member elements of the data stream that correspond to the particular visual zoom level, but not the whole data stream; and the data stream object returning the one or more identified portions of the data stream, the one or more identified portions of the data stream being used in a data-driven model in which one or more view components use the one or more identified portions of the data stream to render one or more visual items on a display.