At the start of “Titian, Tintoretto, Veronese: Rivals in Renaissance Venice,” at the Boston Museum of Fine Arts, is a seventeenth-century map of La Serenissima studded with colored dots, a different hue for each artist.[1] (The color coding repeats on the labels.) The dots mark the artists’ studios and the churches, Scuole, monasteries, and government buildings housing their most important commissions. There’s proximity and even overlap among the sites of the commissions, but the studios are widely spaced, as if each artist were a solitary territorial animal whose powerful aura repelled the others from his range. The map is a graphic metaphor for the entire exhibition, which tracks the complex relationships between three masters whose works, separately and collectively, more or less define what we mean by Venetian painting at its mos ...