The document discusses several applications of matrices. It begins by explaining how matrices can be used to encrypt and decrypt messages by assigning numeric values to letters and performing matrix multiplication. It then discusses how geologists use matrices for seismic surveys to measure properties of the Earth. The document also notes that matrices are used in economics to calculate GDP and model industry output levels. Finally, it mentions that matrices are useful for computer graphics operations like scaling and rotation, and have various other uses in organizing data, engineering reports, and architecture.