The phrase "area which has gained" is correct and usable in written English.
It can be used when discussing a specific field or domain that has experienced growth or improvement over time.
Example: "The area which has gained the most attention in recent years is renewable energy technology."
Alternatives: "field that has developed" or "sector that has expanded".
This paper focuses on one such low energy capability – cooling using groundwater, which has gained popularity in recent years in the London area.
This has, for example, resulted in legislation designed to facilitate progress in orphan drug development which has gained momentum and support in many different areas.
Prime Minister Haider al-Abadi ordered the lifting of restrictions to normalise life and to demonstrate that Baghdad no longer faces a threat from Islamic State, the militant group which had gained control of areas of northern and western Iraq last year.
A few hundred Dutch peacekeepers were stationed in Srebrenica, which had gained the status of a UN-protected "safe area".
Japanese companies have pushed into Africa and Latin America in part by distinguishing themselves from Chinese companies, which have gained a reputation for exploitation in many areas of those continents.
Mr. Arafat previously insisted that he could not act against popular militant groups without some gain in exchange, like an easing of the Israeli blockade of Palestinian areas, which has caused economic hardship.
Talks have been held with imams and community leaders in inner cities, areas which have proved to be lucrative for Islamists in gaining adherents.
The tribal areas, which have always suffered neglect at the hands of the government, will only stand to gain.
For example, there is little data on demographic changes in India, in terms of which areas have gained or lost population and by how much, and Spatocco says "this could be an extremely powerful tool" for analyzing those population shifts by automated tracking of where houses are and how that changes over time.
