Access one element of the map using a single offset value. It is treated as a linear array of elements. That is, the offset can be anywhere between 0 and (width×height)-1. The addressing is row-major meaning that elements 0 through width-1 refer to the first row, width through (2×width)-1 is the second row, etc. This may be used to read the value (in an expression) or to set it (in an assignment statement).