This document describes the content and format of the 52 county boundary .rda datasets integrated in this package for 2000 and 2010 census years. The SeerMapper package contains a set of boundary ".rda" files for the 52 states', D. C.'s and Puerto Rico county or parish sub-areas for both the 2000 and 2010 census year. Each dataset contains the boundary information for all of the county/parish sub-area in that state, district or territory. The dataset name and object name convention used is coXX.dYY, where "co" indicates county boundaries, XX is the state FIPS code and YY is the last 2 digits of the census year (00 or 10). Only three states have a different set of counties and boundaries: Colorado, Alaska, and Washington. Only these states have two county ".rda" files in the package - one for each census year. All other states use the "00" version for both census years.
data(co01_d00)Each dataset contains a SpatialPolygons structure representing the county boundaries for all counties in a single state. Each "polygons" item in the structure represents one county and all of the polygons required to define the county, including lakes, holes, etc. The boundary files are based on the boundaries used in the 2000 and 2010 Census. The coordinates system used in these rda files have been transformed from the census Long/Lat values to an equal area projections for mapping.
Each dataset (.rda file) represents the county boundaries for one state for the 2000 and 2010 U. S. census. In the 2010 census the counties in three states, Alaska, Colorado, and Virginia changed. In all other cases, the 2000 census county boundaries can be reused when mapping 2010 location IDs. To handle the three exceptions, three additional county boundary datasets are included and used by the package when the censusYear is set to 2010 and counties in these states are referenced in the data (at the county or tract level.)
Based on the locations on the rate or category data provided by the user, only needed county boundary information is loaded by the package for the referenced states. The multiple sate boundary data maybe accumulated by the package and used for mapping.
The data formats are the same for each county boundry .rda in this package, a single SpatialPolygons variable. The format of the dataset names is "co", the two digit state FIPS code, "_d", the two digit census year (00 or 10), and ".rda". The SeerMapper package contains the set of boundary datasets for all of the U. S. 2000 Census counties as individual datasets named coXX_d00 and the three additional boundary datasets for the three states where the counties changed in the 2010 census.
Each row.name of the SpatialPolygons is a polygons slot in the data structure and represents a set of Polygons that form the county. The row.names used are the the 5 digit FIPS state/county code associated with the county.
The county information that may normally be carried as a data.frame with a SpatialPolygonsDataFrame is stored in the co99_d00 dataset in the package. This allows the package to all of the county information without having to load the boundary data.
The county boundary information has been transformed from the U. S. Census boundary data's lat/long coordinates under NAD83 to the Alber equal area cartisian coordinates.
The PROJ.4 projection used for transformation of these boundaries is:
"+proj=aea +lat_1=33 +lat_2=49 +lat_0=39 +lon_0=96W +ellps=WGS84"
All boundary data used by SeerMapper were transformed to this projection when the package is constructed.
All the ".rda" files are compressed using the "xy" method to reduce the disk space requirements.
All of the boundary shape file data was imported from the U. S. Census website on July 3, 2016, processed by the urlhttp://www.MapShaper.org website version 01.15 using modified Visvalingam method with intersection repair enabled, prevent shape removal enabled, and a coordinate precision value of 0.0 to simplify the boundaries from 100 space requirements by 90 and edge alignments. The simplified boundaries were then downloaded and converted to SpatialPolygons variables for use by SeerMapper.