For the gallery’s 20th anniversary, Hemphill Fine Arts is throwing everything on the walls. Taking three works each from 30 gallery artists, Hemphill is planning “Represent,” a two-month-long rotating show of the best, the different, and the somewhere-in-between from the gallery’s stable. The place has a lot to celebrate: Even as 14th Street NW is transforming under some higher-order gentrification, Hemphill still stands among the elite tapas restaurants and luxury furniture stores. The gallery has been a cornerstone of the emergent commercial corridor for as long as it’s been heating up. And for good reason: As “Represent” will no doubt show, Hemphill boasts some of the best artists and artworks in the District.