Railroads Commuting traffic 5 Canals 4 Finance 4 Subways 4 Coal mines and mining 3 Coal trade 3 more ... Early works to 1850 3 Gay people 3 Location 3 Maps 3 Roads 3 Appropriations and expenditures 2 Central business districts 2 History 2 Internal improvements 2 Local transit 2 Natural history 2 Transportation 2 %SP6 1 Anthracite coal 1 Cartography 1 Coal 1 Costs 1 Description and travel 1 Historic districts 1 Indian reservations 1 Law offices--Records and correspondence 1 Local transit--Pennsylvania--Philadelphia 1 Mines and mineral resources 1 Overland journeys to the Pacific 1 Railroad 1 Railroads--Management 1 Shippers' guides 1 Sources 1 Street-railroads 1 Surveying 1 Traffic 1 less ...