In this work, we proposed a simple scheme for mapping grid points from one molecular structure to another. Such a mapping allows for a direct visualization of electron density changes (EDC) along the reaction pathway. For six representative reactions, the acquired EDC plots/movies provided intuitive pictures of the (concerted or asynchronous) motion of electrons during the reaction process. Our EDC approach thus provides a handy tool for chemical reaction analysis, which complements many other existing ones in the toolbox (including the recent DVMS method).