Projections for cartographic mapping.
Registry function for adding and accessing projection constructor functions. The type argument is a String indicating the name of the projection type. If the projection argument is not specified, this method returns the matching projection constructor in the registry, or
null if not found. If the projection argument is provided, it must be a projection constructor function to add to the registry under the given type name.
By default, the projection registry includes entries for all projection types provided by the d3-geo module. Projections created using the constructor returned by this method are augmented with the following additional properties:
type: A string value indicating the projection type.
path: A D3 geoPath instance configured to use the projection. When using this path instance, be sure to set the path context as needed.
copy: A zero-argument function the produces a copy of the projection.
// mercator projectionvar mercator = vega;var proj = ;scaletype; // 'mercator'; // [400, 200] center point