What features do places in Mexico share to make a region?

Answer 1

Both regions were part of the same political entity: of New Spain from 1521 until 1821 and of the country of Mexico until 1823 when Central America split up and conformed the Federal Republic of Central America.

This means both regions have approximately the same language, religion, ethnicity and up to some degree, customs and beliefs. On a larger context, both Mexico and Central America belong to Latin America.

Answer 2

In Mexico economic activities, ethnicity and climate are the general guidelines to define a region. For example, the Yucatan peninsula is a tropical region where most people trace their ethnicity to the ancient Mayan civilization and where the main economic activities are tourism and services. On the other hand, northern states such as Monterrey, Chihuahua and Coahuila are of the desert type and it is the region where the most industrialization in Mexico has taken place; also these states have a greater European population and admixture.