Extract US map data to separate package

[pdil]

Currently the data frame which contains coordinates to draw the US state and county boundaries is stored within the usmap package. This data should be extracted into a separate package that can be updated independently of usmap. This will greatly reduce the file size of usmap and will make it easier to develop for with the smaller footprint.

It will also prevent the following NOTE that currently appears during R CMD check (notice extdata size compared to installed size):

> checking installed package size ... NOTE
    installed size is  8.4Mb
    sub-directories of 1Mb or more:
      doc       1.6Mb
      extdata   6.4Mb

To do

• determine name for new package (usmap_data, usmapd, usmapdata, ?) (Extract US map data to separate package #39 (comment))
• create repository for new package (Extract US map data to separate package #39 (comment))
• extract data and tests related to the map data frame (i.e. the us_map function) (Extract US map data to separate package #39 (comment))
• extract data generation scripts (located in data-raw folder) (Extract US map data to separate package #39 (comment))
• submit new package to CRAN (Extract US map data to separate package #39 (comment))
• once uploaded and functional, update usmap to make use of new package instead of internal data (Use usmapdata package #49)

Extra

• consider creating more robust script to download shape files from census.gov and automatically create map data frames This would require automated updating of the county-fips or state-fips files and currently there is no easily parseable document providing this information.

[pdil]

Going with usmapdata as the name since it's clear that it's related to usmap.

[pdil]

Repo created here: https://github.com/pdil/usmapdata

[pdil]

us_map function, data, and tests: pdil/usmapdata@af9c21a

[pdil]

Package has been submitted to CRAN, it will appear here when it's published: https://cran.r-project.org/package=usmapdata