Distance depends on the path definition

This page answers the first question. It uses Vincenty’s inverse method on the GRS80 ellipsoid, which is the ellipsoid used with the Geocentric Datum of Australia 2020. Latitude and longitude define positions on the Earth; the algorithm iteratively solves the ellipsoidal distance and forward bearing.

If the Vincenty iteration does not converge for a rare near-antipodal arrangement, the script falls back to a mean-radius haversine distance and labels that fallback. This is safer than returning an empty or infinite result, but specialised geodesic software is preferable when antipodal precision matters.

Sydney to Melbourne example

The default coordinates represent central Sydney and Melbourne. They produce an ellipsoidal surface distance of about 714 kilometres and an initial bearing generally south-west. A road journey is much longer because highways cannot follow the shortest surface line and must respond to terrain, coast, bridges and the street network.

Read Australian coordinates with the correct signs

Latitude measures north or south of the equator. Australian latitudes are negative in signed decimal degrees because the continent lies in the Southern Hemisphere. Longitude measures east or west of Greenwich; most Australian longitudes are positive because they are east. Sydney therefore appears near latitude −33.87 and longitude +151.21.

Swapping latitude and longitude usually puts a point outside the expected region. Dropping the negative latitude moves an Australian point into the Northern Hemisphere. A single misplaced sign can create a result of thousands of kilometres that is mathematically valid but geographically wrong.

Convert degrees, minutes and seconds before entry

To convert degrees-minutes-seconds to decimal degrees, divide minutes by 60 and seconds by 3,600, then add them to degrees. Apply the negative sign to the whole result for south or west. For example, 33° 52′ 7.68″ south becomes −(33 + 52/60 + 7.68/3600), or approximately −33.8688.

The inputs accept latitude from −90 to +90 and longitude from −180 to +180. More displayed decimal places do not guarantee a more accurate location. Six decimal degrees can suggest sub-metre precision even when the source was a hand-placed map pin several metres or kilometres away.

Initial bearing changes along a geodesic

The displayed bearing is the forward azimuth at Point A, measured clockwise from true north. Zero degrees is north, 90° east, 180° south and 270° west. The compass abbreviation groups the number into one of sixteen familiar directions such as SSW or NE.

Except along special paths, the bearing to remain on the geodesic changes as the journey progresses. The initial bearing is not a constant compass course for a long flight or ocean passage. Magnetic compass headings also differ from true bearings because magnetic declination varies by place and time.

The midpoint is calculated as a spherical geographic midpoint for orientation. It is not an address, road stop or guaranteed halfway point along the ellipsoidal geodesic. For engineering, cadastral, aviation or maritime navigation, use authoritative tools, current charts and the methods required by the relevant regulator.

The planning factor is a scenario, not a route engine

The optional factor multiplies the calculated geodesic. A factor of 1.20 adds 20% to the straight surface distance. It can help create a rough sensitivity range when no route has been chosen, but the correct detour varies enormously. A grid of urban roads may be close to the geodesic; a mountain, river crossing or sparse outback network can create a much larger difference.

Driving distance requires a routable road graph, legal turn restrictions, one-way streets, ferry choices, closures and vehicle constraints. A heavy truck, caravan or oversize load can have a different route from a passenger car. The generic “driving distance calculator Australia” keyword therefore remains a separate intent and is not claimed by this coordinate page.

Flight distance can also differ. Airlines use routes shaped by airways, winds, restricted airspace and operational requirements. Airport coordinates should be used rather than city-centre presets. For fuel or fare planning, use the actual operator route and reserve rules.

Coordinate precision sets a practical accuracy ceiling

At the equator, one decimal degree of latitude is roughly 11 kilometres, 0.01 degree about 1.1 kilometres and 0.00001 degree about a metre. Longitude spacing narrows with latitude. A calculation reported to a metre cannot repair coordinates rounded to a kilometre.

Use the output at a precision appropriate to the source. City-centre presets support a broad intercity comparison, not boundary or property measurement. Survey work should use the Australian Geospatial Reference System, suitable transformations and qualified professional practice.

Build a reproducible coordinate comparison

Record what each point represents before copying coordinates. A town centroid, postcode centroid, station entrance, airport reference point and property gate can all carry the same place name while producing different distances. For emergency access or freight, the practical entrance matters more than the visual centre of a parcel.

Copy latitude and longitude together and retain enough decimal places from the source. Paste the pair into the correct fields, check the signs, and use a map preview from the source system to confirm the pin. After calculation, swap the points: distance should remain the same, while the initial bearing normally changes because it is now measured from the other end.

If two systems disagree, compare five things before comparing formulas: the exact point coordinates, datum, distance type, Earth model and output unit. One service may use a postcode centroid and a road route, another an address rooftop and a sphere, and this page an ellipsoid. A difference is not necessarily a defect when the underlying questions differ.

Altitude is not included

The two-dimensional geodesic follows the reference ellipsoid and does not add height difference. For nearby points with a large vertical separation, a three-dimensional straight-line distance would combine horizontal separation with elevation difference. For long surface routes, terrain profile matters far more than a simple endpoint height adjustment. Obtain compatible ellipsoidal or Australian Height Datum values before attempting a precise three-dimensional calculation.