Methods for studying the geometry of radiating and concentric features are described and compared. The method favoured for radiating features is to assume that the straight lines, which represent the trends of the features, are of infinite length. Then, for each point on a grid, calculating the mean of the perpendicular distances from the point to each of the lines. These values are then contoured, and a centre minimizing the value of the mean estimated visually. The methods are applied to finding the centre of the Lyttelton volcano [New Zealand] from the external contours and finding a radiation centre for its radial dykes.

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