I assume that the underlined phrase here is "which is located between Libya and Morocco." So, what exactly is this phrase? We know that it DOES contain a relative pronoun. We also know that it is an adjective clause, a phrase that describes the preceding noun (Algeria). So it is an essential or a non-essential adjective clause? Well, the reader does not necessarily need to know the location of Algeria to understand what the speaker is talking about. So, it would fall under the category of "nonessential adjective clause."
