Gravity of Earth Gravity acceleration is a vector quantity. In a spherically symmetric Earth, gravity would point directly towards the sphere's centre. As the Earth is slightly flatter, there are consequently slight deviations in the direction of gravity. Tools exist for calculating the strength of gravity at various cities around the world. The effect of latitude can be clearly seen with gravity in high-latitude cities: Anchorage (9.826 m/s), Helsinki (9.825 m/s), being about 0.5% greater than that in cities near the equator: Kuala Lumpur (9.776 m/s), Manila (9.780 m/s). The effect of altitude can be seen in Mexico City (9.776 m/s; altitude ),
Latitude coordinate system. The relation of Cartesian and ellipsoidal coordinates is discussed in Torge. Astronomical latitude () is the angle between the equatorial plane and the true vertical at a point on the surface. The true vertical, the direction of a plumb line, is also the direction of the gravity acceleration, the resultant of the gravitational acceleration (mass-based) and the centrifugal acceleration at that latitude. Astronomic latitude is calculated from angles measured between the zenith and stars whose declination is accurately known. In general the true vertical at a point on the surface does not exactly coincide with either the normal