Just adding a little bit to what other members have answered, since "fronterizo" is an adjective that means "near the border", you can use it on other nouns other than "zona" if you wish to express yourself a bit differently. For example, you can say:
"ciudad fronteriza" ( or the plural "ciudades fronterizas" )
"tierras fronterizas" ( "tierras" meaning lands )
"territorio fronterizo" ( or the plural "territorios fronterizos")
"región fronteriza" ( or "regiones fronterizas" )
I think this might help you broaden your capabilities of expression in Spanish. Good luck with your essay!