Complete Reference on Mathematics at the senior undergraduate or graduate level

Question

I am looking for an alternative book on major topics of Mathematics- a "handbook", much like the "Princeton's Companion to Mathematics" (by Timothy Gowers).

Answer 1

I finally got the "What is Mathematics" book by Richard Courant and Ian Stewarts, which I am highly impressed with. Provides a broad yet simple (medium-technical) view of many important topics like Algebraic Geometry, Topology, etc. A must handbook of all scientists using tools from maths extensively.