～は～が～A whole and its feature
This pattern makes a person, animal, place, or thing the overall topic with は, then describes one of its parts or characteristic aspects with が.
How the two levels work
The phrase before は gives the larger frame: who or what you are talking about. The phrase before が identifies the particular part or aspect being described. The topic particle is written は but pronounced わ.
People, places, and things
The relationship should be easy to recognize: hair is a feature of a person, roads are an aspect of a town, and rooms are part of a hotel.
Symptoms and omitted topics
For a symptom, the person can be the explicit topic. In an immediate conversation, however, it is often obvious that the speaker means their own body, so the topic may be left unsaid.
Making the whole or the part the topic
姉は髪が長いです makes the sister the overall topic and describes her hair. 姉の髪は長いです makes the hair itself the immediate topic. The factual message can be similar, but the listener's attention is organized differently.