1. 2010 Census, 2010. 〈Http://www.Census.Gov/2010census/〉.
2. A retrospective investigation of pm10 in ambient air and cardiopulmonary hospital admissions in Allegheny County, Pennsylvania: 1995–2000;Arena;J. Occup. Environ. Med./Am. Coll. Occup. Environ. Med.,2006
3. Arnold, J., Daroczi, G., Werth, B., Weitzner, B., Kunst, J., Auguie, B., et al., 2016. Extra themes, scales and geoms for 'ggplot2'.
4. Baquero, O., 2016. North symbols and scale bars for maps created with 'ggplot2' or 'ggmap'.
5. Becker, R., Wilks, A., 2016. Original s code r version by ray brownrigg. Enhancements by thomas p minka and alex deckmyn.