A distinction has to be made between primary and secondary chakras, as these are very often confused.
The primary chakras are the inner chakras, i.e. the chakras as described by original Tantra (Shaktism, Nathism, etc), which can only be accessed through deep yogic practice. These chakras are archetypal and do not have a form; the form they are represented as in tantric literature is stylised and symbolic. Now do they have a precise location. They are associated with specific correspondences including mantric vibrations, elements, gods, etc.
The primary chakras are represented in an up-down vertical axis (the microcosmic “Mount Meru” – world mountain), and are polarised according to Shiva (pure unmanifest Consciousness, the Godhead) and Shakti (the power of manifestation). Shakti is represented by the Kundalini energy at the base of the spine, or more strictly speaking, in the Muladhara chakra (which as with all the Primary Chakras does not have a strict physical location). Shiva is located in the crown chakra (Saharsrara) at the crown above the head. This vertical polarisation represents the major planes of existence
As microcosmic archetypes the primary chakras can be equated with the ten sefirot of Kabbalah, which are arranged, significantly, in seven rows. Various schemes and suggestions have been made to equate the two, but none are completely satisfactory.