So he carried me away in the spirit into the wilderness; and I saw a woman sit upon a scarlet colored beast, full of names of blasphemy, having seven heads and ten horns.
The most interesting area of study of Revelation 17 and 18 are translating the English interpretations back into the original Greek and breaking down the meaning behind those words. Some of the English translations were poorly chosen.
John chose his words very carefully when drafting his account, detailing specifics that are not found in the English translations. Studying the Greek which John used gives us a clearer picture of what John was witnessing while in the spirit.
In verse 7 the angel tells John that he will tell him the mystery of the woman and the beast (kingdom) that carries her. The angel begins to give John a succession of events surrounding the beast that carries the woman upon his seven heads. It seems as though the angel completely skips telling John about the woman until we reach chapter 18. The angel begins with the beast in verse 8 but does not give John much more information concerning the city itself until the very last verse, Revelation 17:18. This final verse transitions chapter 17 into chapter 18. (chapter breaks were not added until the Geneva Bible was printed in 1557) Here, the angel tells John that the woman which he saw was that great (μεγας) city (πολις) which reigns over the kings of the earth.
In the Greek the words that he uses are μεγας, mega meaning great. When defined in the Greek μεγας means huge, enormous by volume, overtly large by physical size.
πολις or, polis for city is defined in the Greek as a walled city, mother city, magistrate city of many that dominates well defined territory.
So now we know that the woman is a metaphor for a extremely large city.