I am working on a project utilizing free data from http://www.pasda.psu.edu/, specifically data from PennDot, 2015 Pennsylvania County Boundaries http://www.pasda.psu.edu/uci/MetadataDisplay.aspx?entry=PASDA&file=PaCounty2015_01.xml&dataset=24. I would like to know why a particular county would appear wider than a printed 2008 PennDOT Major Highway map of the same county that I have seen before (basically I just want to know how to explain this if asked). Whenever I view the layer properties for the county boundaries layer I have added into ArcGIS, it shows that it is a geographic coordinate system of NAD83_GEO, so therefore from my understanding not a projected coordinate system that has a particular projection associated with it? When I look at the PennDot highway map from 2008 it states that it is a Polyconic Projection-NAD 83 Datum.
Is it because this particular, current data from 2015 I am using for my map happens to not have a projection assoicated with it like the highway map, which says it is a Polyconic Projection? The differences between the projected coordinate system NAD 1983 and geographic coordinate system NAD 1983 confuse me!
Essentially I want to know what, if anything, would be the differences between a printed map that is Polyconic Projection-NAD 83 Datum and the county boundary shapefile I am trying to utilze, which is geographic coordinate sytem of NAD83_GEO.