# Cassini

## Description

The Cassini is a transverse cylindrical equidistant projection. The projection maintains scale along the central meridian and all lines perpendicular to the central meridian. The Cassini projection is analogous to the plate carrée projection in the same way the transverse Mercator projection is to the Mercator projection.

The Cassini projection was developed by César-François Cassini de Thury in 1745. More accurate equations for an ellipsoid of revolution were developed later by Johann G. von Soldner in 1810. Therefore, the projection is also known as Cassini-Soldner. It is available in ArcGIS Pro 1.0 and later and in ArcGIS Desktop 8.0 and later.

## Projection properties

The subsections below describe the Cassini projection properties.

### Graticule

The Cassini projection is a transverse cylindric projection. The equator, central meridian, and meridians 90° from the central meridian project as straight lines. Other meridians project as complex curves concave toward the central meridian and perpendicularly intersect with the equator. Other parallels are also complex curves, concave toward the nearest pole. Both poles project as points. The graticule is symmetric across the equator and the central meridian.

### Distortion

The projection is equidistant along the central meridian and all lines perpendicular to it. There is no distortion along the central meridian. Shape, area, direction, and angle distortion increase with the distance from the central meridian. Distortion values are symmetric across the equator and the central meridian.

## Usage

This projection is appropriate for large-scale maps with predominantly north-south extents. It was used by the Ordnance Survey of Great Britain and some German states in the late nineteenth century. It was also used in Cyprus, former Czechoslovakia, Denmark, Malaysia, and the former Federal Republic of Germany. The transverse Mercator projection is typically preferred over the Cassini projection because it presents relatively less scale and direction distortion.

## Limitations

The Cassini projection in ArcGIS projects data within 45° from the central meridian only and does not display the antimeridian due to math instability.

## Parameters

Cassini parameters are as follows:

• False Easting
• False Northing
• Central Meridian
• Scale Factor
• Latitude Of Origin

## Sources

Snyder, J. P. (1987). Map Projections: A Working Manual. U.S. Geological Survey Professional Paper 1395. Washington, DC: United States Government Printing Office.

Snyder, J. P. (1993). Flattening the Earth. Two Thousand Years of Map Projections. Chicago and London: University of Chicago Press.

Snyder, J. P. and Voxland, P. M. (1989). An Album of Map Projections. U.S. Geological Survey Professional Paper 1453. Washington, DC: United States Government Printing Office.