1. To make a quick, rough drawing of something, especially as a detail or element of a larger work. A noun or pronoun can be used between "sketch" and "in." They asked me to sketch in a few people to make the painting of the park feel more real. She sketched some popular tourist locations in on my map.

2. To present or write smaller details or aspects of a larger thing. A noun or pronoun can be used between "sketch" and "in." We really liked your proposal, but we were hoping you could sketch in a few more specifics before we sign off on it.