Horter was born in Germantown, Philadelphia. He was a self-taught artist who engraved stock certificates as a teenager. A superb draftsman and technician, Horter was first employed as a commercial artist working for N.W. Ayer, the largest advertising agency in Philadelphia and third largest in the country. Throughout his career, Horter produced a tremendous body of work consisting of drawings, lithographs, and etchings that depict large cities such as Philadelphia and New York.