Mathematicians certainly can. https://en.wikipedia.org/wiki/Taxicab_geometry#Balls https://en.wikipedia.org/wiki/Taxicab_geometry#Balls: “A topological ball is

Mathematicians certainly can. https://en.wikipedia.org/wiki/Taxicab_geometry#Balls https://en.wikipedia.org/wiki/Taxicab_geometry#Balls: “A topological ball is a set of points with a fixed distance, called the radius, from a point called the center. In n-dimensional Euclidean geometry, the balls are spheres. […] In n dimensions, a taxicab ball is in the shape of an n-dimensional orthoplex. In two dimensions, these are squares with sides oriented at a 45° angle to the coordinate axes.”