Interfacing 1990 US Census TIGER map files with New S graphics software

Abstract

In 1990, the United States Bureau of the Census released detailed geographic base files known as TIGER/Line (Topologically Integrated Geographic Encoding and Referencing) which contain detail on the physical features and census tract boundaries of every county in the United States. The TIGER database is attractive for two reasons. First, it is publicly available through the Bureau of the Census on tape or cd-rom for a minimal fee. Second, it contains 24 billion characters of data which describe geographic features of interest to the Census Bureau such as coastlines, hydrography, transportation networks, political boundaries, etc. Unfortunately, the large TIGER database only provides raw alphanumeric data; no utility software, graphical or otherwise, is included. On the other hand New S, a popular statistical software package by AT&T, has easily operated functions that permit advanced graphics in conjunction with data analysis. New S has the ability to plot contours, lines, segments, and points. However, of special interest is the New S function map and its options. Using the map function, which requires polygons as input, census tracts can be quickly selected, plotted, shaded, etc. New S graphics combined with the TIGER database has obvious potential. This paper reports on our efforts to use the TIGER map files with New S, especially to construct census tract maps of counties. While census tract boundaries are inherently polygonal, they are not organized as such in the TIGER database. This conversion of the TIGER ``line`` format into New S ``polygon/polyline`` format is one facet of the work reported here. Also we discuss the selection and extraction of auxiliary geographic information from TIGER files for graphical display using New S.