Top: The contact angle (θ), defined as the angle between lines joining the point of contact between two microtubules and their respective minus ends, is an important geometrical feature that regulates microtubule coalignment. (i) A microtubule tip that encounters a lattice at a shallow angle (θ < 40°) gets cross-linked with the lattice and continues growing (top), while a microtubule that makes a steep angle (θ > 40°) undergoes collision-induced catastrophe (bottom). (ii) The probability of occurrence of microtubule tip-guiding events is determined by the contact angle (θ). Top: Tip guiding is mediated by motile kinesins (magenta) and +tip binding proteins (green). Guiding occurs through polymer bending at high contact angles (θ > 85°). Bottom: At intermediate angles (40° < θ < 85°), the need for continuous MAP occupancy of the newly polymerized tip (light green lattice) causes slippage events which decrease guidance probability.