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The Molecules with ALMA at Planet-forming Scales (MAPS) Large Programprovides a unique opportunity to study the vertical distribution of gas,chemistry, and temperature in the protoplanetary disks around IM Lup, GM Aur,AS 209, HD 163296, and MWC 480. By using the asymmetry of molecular lineemission relative to the disk major axis, we infer the emission height ($z$)above the midplane as a function of radius ($r$). Using this method, we measureemitting surfaces for a suite of CO isotopologues, HCN, and C$_2$H. We findthat $^{12}$CO emission traces the most elevated regions with $z/r > 0.3$,while emission from the less abundant $^{13}$CO and C$^{18}$O probes deeperinto the disk at altitudes of $z/r \lesssim 0.2$. C$_2$H and HCN have loweropacities and SNRs, making surface fitting more difficult, and could only bereliably constrained in AS 209, HD 163296, and MWC 480, with $z/r \lesssim0.1$, i.e., relatively close to the planet-forming midplanes. We determine peakbrightness temperatures of the optically thick CO isotopologues and use theseto trace 2D disk temperature structures. Several CO temperature profiles andemission surfaces show dips in temperature or vertical height, some of whichare associated with gaps and rings in line and/or continuum emission. Thesesubstructures may be due to local changes in CO column density, gas surfacedensity, or gas temperatures, and detailed thermo-chemical models are necessaryto better constrain their origins and relate the chemical compositions ofelevated disk layers with those of planet-forming material in disk midplanes.This paper is part of the MAPS special issue of the Astrophysical JournalSupplement.

Molecules with ALMA at Planet-forming Scales (MAPS) IV: Emission Surfaces and Vertical Distribution of Molecules