MS Visio is a professional diagramming tool which can work both with manually created shapes and with ready shapes. This ready shapes are collected in stencils. Visio has lots of stencils with ready shapes on a variety of thematics.
Each shape is represented both in Metric format of dimensions and in US (inches) format.
Many of such ready shapes have unique features added with using of formulas of internal Visio programming language. For example, they can automatically stretch to fit some area or text. Despite the fact that Visio have lots stencils with shapes they are black-and-white in most cases.
So if you want to create a diagram with lots of color shapes, you need to find something else.
ConceptDraw is an alternative for Visio both on PC and Mac and in contrast to Visio ConceptDraw has a set of libraries (analog of Visio stencils) with beatiful coloured shapes. This distinction is especially noticeable in ConceptDraw libraries and Visio stencils assigned for Landscape design.
ConceptDraw shapes also supports formulas and custom properties for all shapes. ConceptDraw uses its own internal CDBasic for formulas. So you can import Visio shapes to ConceptDraw and export ConceptDraw shapes to Visio but all “smart” properties given by formulas will be lost.