Square Kilometre

The square kilometre (American English: square kilometer; symbol: km²) is a metric unit of surface area used internationally to measure large expanses of land, water and built environments. It is derived from the square metre, the base SI unit of area, and represents the area of a square whose sides each measure one kilometre. Owing to its convenient size and ease of conversion, it is among the most widely used units for describing geographical regions and significant territorial or infrastructural features.
One square kilometre consists of 1,000,000 square metres or 100 hectares, placing it at the intersection of agricultural, geographical and scientific measurement systems. The unit is also commonly compared with imperial measures, equating to roughly 0.3861 square miles or 247.1 acres.

Definition and Conversions

The formal relationships between the square kilometre and related units are:

• 1 km² = 1,000,000 m²
• 1 km² = 100 hectares (ha)
• 1 km² ≈ 0.3861 square miles
• 1 km² ≈ 247.1 acres

Conversely:

• 1 m² = 10⁻⁶ km²
• 1 hectare = 0.01 km²
• 1 square mile ≈ 2.59 km²
• 1 acre ≈ 0.004047 km²

Importantly, km² denotes “square kilometre” and not “kilometre multiplied by square metre”. Thus, 3 km² equals 3,000,000 m², not 3,000 m².

Use in Topographical Mapping

Topographical maps often employ kilometre-based grid systems to simplify measurement. Grid lines are typically spaced one kilometre apart, creating uniform squares that each represent 1 km² on the ground.
Depending on map scale:

• 1:100,000 maps feature 1-cm² grid squares each representing 1 km².
• 1:50,000 maps use 2-cm by 2-cm grid squares.
• 1:25,000 maps use 4-cm by 4-cm grid squares.

Such grids assist with navigation, land assessment and spatial planning.

Medieval City Centres

Many medieval European cities developed within defensive walls enclosing roughly one square kilometre. Although their shapes were seldom perfect rectangles or circles, their areas can be estimated by fitting the wall outline to simple geometrical figures.
Examples include:

• Delft (Netherlands): An approximately rectangular walled area close to 0.9 km².
• A medieval Italian city: Rectangular in form, with an estimated area of around 1.09 km².
• Bruges (Belgium): Oval in shape, with an area of approximately 3.6 km² for the historic core.
• Chester (UK): A compact walled city with an area near 0.5 km².

These illustrative cases show how one square kilometre corresponds closely with the scale of many pre-modern urban centres.

Parks and Recreational Areas

Several public parks approach or match one square kilometre in size, making them practical reference points for visualising the unit. Examples include parks in the United Kingdom, the United States, Canada, Poland and Australia. Larger recreational complexes, such as Sydney Olympic Park, contain multiple square kilometres of dedicated land, including over six square kilometres of wetlands and waterways.

Golf Courses

Standard eighteen-hole golf courses require significant land area. Based on typical fairway and safety-zone dimensions, a course usually occupies around 80 hectares, or 0.8 km², placing it close to the scale of one square kilometre. Numerous courses worldwide reflect this typical land allocation.

Other Areas Approximating One Square Kilometre

A variety of institutional, industrial and natural areas also measure close to this size, such as:

• Science and technology parks
• Industrial estates
• University and school campuses
• Small islands