Functions like GridSpec("LLC90") return a gcmgrid struct that contains the basic specification of a global grid. This is not the grid itself -- just a few parameters, ranges, and possibly a path to grid files. A gcmgrid is embeded in each MeshArray instance for which it provides a blueprint. It specifies how an array collection forms a global mesh and allows e.g. the exchange function to dispatch to the appropriate method.
Various configurations that are commonly used in Earth System Models are readily implemented using the concrete type called MeshArray. This type is in fact an alias for more specific types that can be used interchangeably via MeshArray (initially: gcmfaces or gcmarray).
Within a MeshArray, a whole Earth System Model grid is represented as an array of elementary arrays. Each one of these represents a subdomain. For example, a gcmarray instance for one Earth map x has a column array x.f of elementary 2D arrays of various sizes.
The [basics tutorial](@ref id_Basics) illustrates how standard operations apply to MeshArray like as they do to common Array. More specialized functions and distinctive features, such as domain decomposition or plotting maps, are demo'ed in the [geography tutorial](@ref id_Geography) and [vector tutorial](@ref id_Vectors).
The origin of MeshArrays.jl is rooted in a Matlab / Octave package called gcmfaces, which was introduced in Forget et al., 2015 (doi:10.5194/gmd-8-3071-2015). GCM is an acronym for General Circulation Model, or Global Climate Model, and faces can be equivalent to meshes, arrays, facets, or subdomains (these are the elements of x.f in a MeshArray instance x).