Square kilometre (International spelling as used by the International Bureau of Weights and Measures) or square kilometer (American spelling), symbol km2, is a multiple of the square metre, the SI unit of area or surface area. 1 km2 is equal to: 1,000,000 square metres (m2) 100 hectares (ha) It is also approximately equal to: 0.3861 square miles 247.1 acres Conversely: 1 m2 = 0.000001 (10−6) km2 1 hectare = 0.01 (10−2) km2 1 square mile = 1 acre = about The symbol "km2" means (km)2, square kilometre or kilometre squared and not k(m2), kilo–square metre. For example, 3 km2 is equal to = 3,000,000 m2, not 3,000 m2. Examples of areas of 1 square kilometre Topographical Map grids Topographical map grids are worked out in metres, with the grid lines being 1,000 metres apart. 1:100,000 maps are divided into squares representing 1 km2, each square on the map being one square centimetre in area and representing 1 km2 on the surface of the earth. For 1:50,000 maps, the grid lines are 2 cm apart. Each square on the map is 2 cm by 2 cm (4 cm2) and represents 1 km2 on the surface of the earth. For 1:25,000 maps, the grid lines are 4 cm apart. Each square on the map is 4 cm by 4 cm (16 cm2) and represents 1 km2 on the surface of the earth. In each case, the grid lines enclose one square kilometre. Medieval city centres The area enclosed by the walls of many European medieval cities were about one square kilometre. These walls are often either still standing or the route they followed is still clearly visible, such as in Brussels, where the wall has been replaced by a ring road, or in Frankfurt, where the wall has been replaced by gardens. The approximate area of the old walled cities can often be worked out by fitting the course of the wall to a rectangle or an oval (ellipse). Examples include Delft, Netherlands (See map alongside) The walled city of Delft was approximately rectangular. The approximate length of rectangle was about . The approximate width of the rectangle was about . A perfect rectangle with these measurements has an area of 1.30×0.75 = 0.9 km2 Lucca (Italy) The medieval city is roughly rectangular with rounded north-east and north-west corners. The maximum distance from east to west is . The maximum distance from