Philadelphia's central city was created in the 17th century following the plan by William Penn's surveyor Thomas Holme. Center City is structured with long straight streets running east-west and north-south forming a grid pattern. The original city plan was designed to allow for easy travel and to keep residences separated by open space that would help prevent the spread of fire. The Delaware River and Schuylkill Rivers served as early boundaries between which the city's early street plan was kept within. In addition, Penn planned the creation of five public parks in the city which were renamed in 1824 (in parenthesis): Centre Square, North East Publick Square (Franklin Square), Northwest Square (Logan Square), Southwest Square (Rittenhouse Square), and Southeast Square (Washington Square). Center City has grown into the second-most populated downtown area in the United States, after Midtown Manhattan in New York City, with an estimated 183,240 residents in 2015.