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Deuterium fractionation is dependent on various physical and chemicalparameters. Thus, the formation location and thermal history of material in thesolar system is often studied by measuring its D/H ratio. This requiresknowledge about the deuteration processes operating during the planet formationera. We aim to study these processes by radially resolving the DCN/HCN (at 0.3"resolution) and N$_2$D$^+$/N$_2$H$^+$ (0.3 to 0.9") column density ratiostoward the five protoplanetary disks observed by the Molecules with ALMA atPlanet-forming scales (MAPS) Large Program. DCN is detected in all fivesources, with one newly reported detection. N$_2$D$^+$ is detected in foursources, two of which are newly reported detections. We derive column densityprofiles that allow us to study the spatial variation of the DCN/HCN andN$_2$D$^+$/N$_2$H$^+$ ratios at high resolution. DCN/HCN varies considerablyfor different parts of the disks, ranging from $10^{-3}$ to $10^{-1}$. Inparticular, the inner disk regions generally show significantly lower HCNdeuteration compared with the outer disk. In addition, our analysis confirmsthat two deuterium fractionation channels are active, which can alter the D/Hratio within the pool of organic molecules. N$_2$D$^+$ is found in the coldouter regions beyond $\sim$50 au, with N$_2$D$^+$/N$_2$H$^+$ ranging between$10^{-2}$ and 1 across the disk sample. This is consistent with the theoreticalexpectation that N$_2$H$^+$ deuteration proceeds via the low-temperaturechannel only. This paper is part of the MAPS special issue of the AstrophysicalJournal Supplement.

Molecules with ALMA at Planet-forming Scales (MAPS). X. Studying deuteration at high angular resolution toward protoplanetary disks