MAPL is a software layer and set of conventions to standardize the use of the ESMF. The core of the MAPL software was originally developed at NASA Goddard Space Flight Center by Max Suarez and Atanas Trayanov, in an effort to facilitate the use of ESMF in support of the modeling activities of the Global Modeling and Assimilation Office).
Today, the most complete implementation of MAPL is the code used to create the GEOS-5 modeling and assimilation system. The GEOS-5 atmospheric model consists of a hierarchy of numerical and computational modules, each an ESMF Gridded Component.
MAPL provides mechanisms to easily write new Gridded Components or to encapsulate, or "wrap", legacy codes as ESMF Gridded Components. It also provides the means to wire the components together into hierarchies, such as the one shown in the figure. MAPL is mostly decoupled from the components' numerical and computational aspects. This means that MAPL can be used with arbitrary codes as a simple way to generate an ESMF component interface. The attached pdf document, An Introduction to MAPL, provides details on its overall design and usage.