Linked from
The 15 pages that link to Coordinate chart, each with the reason it gives.
Metric tensorRelated: Metric components are expressed in coordinates and transform between charts.
Tangent spaceRelated: Charts provide coordinates for computing tangent vectors.
Christoffel symbolsRelated: The symbols depend on the chart used to express the connection.
Tensor fieldRelated: Charts let tensor fields be written as component functions.