D.C. Mun. Regs. tit. 23, r. 23-101
In establishing a geographic boundary, including the designations of locality, section, or portion set forth in the Act or this title, the Board shall measure the specified distance in an arc from each corner of the building on which the licensed establishment is located, connecting the arcs by tangent lines.
In establishing the distance between one or more places, (such as the actual distance of one licensed establishment from another or the actual distance of a licensed establishment from a school), the distance shall be measured linearly by the Board and shall be the shortest distance between the property lines of the places.
If a boundary line measured by the Board touches upon any portion of a parcel or lot, the parcel or lot shall be within the area being identified by the Board.
D.C. Mun. Regs. tit. 23, r. 23-101