Real (or complex) n-dimensional projective space can be considered as ℝⁿ (or ℂⁿ) together with points at infinity (specifically, a hyperplane at infinity). In terms of homogeneous coordinates, points [1:x₁:…:x_n] can be identified with ℝⁿ and the hyperplane has equation x₀ = 0. From the point of view of affine geometry, these points at infinity will remain at infinity; from the projective view, the points at infinity are no different from other points, and the hyperplane at infinity need not be invariant under a projective transformation. Topologically, the real projective line is the circle, and the complex projective line is the Riemann sphere.