Simplify the following text for a Grade 7 native English-speaking person.
Original: The 20 largest urban areas are Greater London Urban Area , West Midlands Urban Area , Greater Manchester Urban Area , West Yorkshire Urban Area , Greater Glasgow , Tyneside , Liverpool Urban Area , Nottingham Urban Area , Sheffield Urban Area , Bristol Urban Area , Greater Belfast , Brighton\/Worthing\/Littlehampton , Edinburgh , Portsmouth Urban Area , Leicester Urban Area , Bournemouth Urban Area , Reading\/Wokingham Urban Area , Teesside , The Potteries Urban Area and Coventry\/Bedworth Urban Area
Simplified: Urban area is a word from geography . In an urban area , the population density ( how many people live in a certain area ) is higher than in the surrounding area .