04-manifold.Rmd

# The Manifold GIS model

## Drawings are points, lines, and areas

Manifold drawings can contain all three kinds of vector topology. Other formats that can do this are MapInfo, SDTS (?), KML, etc. ..

## Manifold projects are single-file documents

The main reason this is nice is that we can easily encapsulate a body of work in a single file and shared it, without having to trace complicated sets of files. We can also treat a project document as database. (There are other ways to deal with Manifold via database technology.)

## Connecting to Manifold with R

### Complications

Manifold uses its own internal specification for map projections. It can convert to WKT. R's package `rgdal` uses PROJ.4 strings which generally do not store sufficent detail to enable round-tripping. 

R's Spatial classes need separate objects for different topological types.