The process of urbanization — land or an area becoming urban in character, such as being developed for housing or commerce; often used in legal/zoning contexts (can be used as 'to urbanize').
その地域は近年急速に市街化して、商業施設が増えた。
That area has rapidly urbanized in recent years and commercial facilities have increased.
市街化に伴って公共交通の整備が必要になった。
With urbanization, development of public transportation became necessary.
都市計画では、どの地域を市街化するかをあらかじめ決めることが重要だ。
In urban planning, it's important to decide in advance which areas will be urbanized.