隣接 and 接近: a neighboring arrangement and an approach
Compare adjacent villages with model trains that approached each other, distinguishing an existing arrangement from movement closer.
A neighboring arrangement in 隣接
隣接（りんせつ） describes neighboring places. 「二つの町は隣接しているが、交通手段が少ない。」 says that the villages are adjacent but have few means of transportation. 隣接している presents their existing spatial relationship.
「図書館に隣接する公園で昼食を取った。」 also presents the library and park as adjoining places. Eating lunch is the stated action, while adjacency is information about the park's location.
Movement closer in 接近
接近（せっきん） means approach. 「二台の模型列車がゆっくり接近した。」 says that the two model trains slowly approached each other. 接近した presents movement closer.
ゆっくり describes how they approached without giving an exact speed. Approaching does not state that the trains touched or became a single train.
The extent of the comparison
隣接 in the village example describes a neighboring spatial relationship. 接近 in the train example describes movement closer. Scarce transportation does not negate the villages' adjacency.
The examples do not restrict 隣接 to stationary objects or define 接近 as completed contact. They distinguish the arrangement and the movement presented in each sentence.
Does 二台の模型列車がゆっくり接近した。 alone establish that the two trains already touched?
Show the answer and why
No. It reports a slow approach, not actual contact. This also differs from the neighboring arrangement described by 隣接.