Vector space to affine: isomorph, one-to-one Pts, lines, parallelism vector to Euclidean as an enrichment: scalar prod Angle, distances, circles affine to projective as an extension add ideal elements Pts at infinity10 • Vector space to affine: isomorph, one-to-one • vector to Euclidean as an enrichment: scalar prod. • affine to projective as an extension: add ideal elements Pts, lines, parallelism Angle, distances, circles Pts at infinity