I'm currently working with a road network where each segment is defined by a Name, a BeginLog, and an EndLog. These log values are rigorously measured using driving distance. However, when I compare the segment length using LengthCalculator vs the measured length (EndLog - BeginLog), the LengthCalculator distances are consistently greater by 25%-30%.
Feature source = SQL Server; Geometry = shapefile; Source projection = Mercator Aux Sphere; FME projection (from FME Inspector) = Spherical Mercator; Measured length = miles converted to feet using 5280 ft/mile; LengthCalculator = meters converted to feet using 3.28084 ft/meter; road network is in Ohio, so impact of altitude on driving distance is minimal.
I've checked my conversions and they seem to be OK.I don't have formal GIS training, so I'm stumped by the differences between the two methods. Can someone please help me understand what's going on?Thanks!