The Southside is not an official administrative area but a colloquial term. To some, especially those from outside Dublin, the Southside of Dublin is presumed to be the area within Dublin's county borders bounded to the north by the River Liffey. To native Dubliners, however, the socio-cultural particularities of the 'southside' and 'southsiders' are not contained within this artificial construct.
Southside is the colloquial name given to a broad swath of southeastern and/or south-central Virginia, USA. It is bounded on the north by the James River, the south by the North Carolina border, the west by the Blue Ridge Mountain Foothills and to the east (generally) the fall line.
South Side (two words) is a neighborhood in the city of Pittsburgh, USA. The South Side is traditionally divided into two neighborhoods, South Side Flats and South Side Slopes. The population of the Flats was 5726 in the 2000 census.http://www.city.pittsburgh.pa.us/cp/assets/census/southsideflats.pdf The population of the Slopes was 5007http://www.city.pittsburgh.pa.us/cp/assets/census/southsideslopes.pdf.