To what does the term “linkage” refer?

The term linkage is referred to economic geographic.  

Explanation:

This term refers portray interfirm interdependence.

For others authors Linkages are the interactions and relationships between tasks, functions, departments   and organizations.

In another context these kind of interactions do allow and promote the flow of information and ideas in achieving the objectives of the tourism business.  

answers.com says temperate reagions

because the two particles have an equal charge, the charges will cancel out and give the atom an overall charge of 0. so, if at atom has 35 protons in the nucleus, we could expect it to have 35 electrons orbiting that nucleus.