  We present Ha maps at 1kpc spatial resolution for star-forming galaxies at
z~1, made possible by the WFC3 grism on HST. Employing this capability over all
five 3D-HST/CANDELS fields provides a sample of 2676 galaxies. By creating deep
stacked Halpha (Ha) images, we reach surface brightness limits of
1x10^-18\erg\s\cm^2\arcsec^2, allowing us to map the distribution of ionized
gas out to >10kpc for typical L* galaxies at this epoch. We find that the
spatial extent of the Ha distribution increases with stellar mass as
r(Ha)[kpc]=1.5(Mstars/10^10Msun)^0.23. Furthermore, the Ha emission is more
extended than the stellar continuum emission, consistent with inside-out
assembly of galactic disks. This effect, however, is mass dependent with
r(Ha)/r(stars)=1.1(M/10^10Msun)^0.054, such that at low masses r(Ha)~r(stars).
We map the Ha distribution as a function of SFR(IR+UV) and find evidence for
`coherent star formation' across the SFR-M plane: above the main sequence, Ha
is enhanced at all radii; below the main sequence, Ha is depressed at all
radii. This suggests that at all masses the physical processes driving the
enhancement or suppression of star formation act throughout the disks of
galaxies. It also confirms that the scatter in the star forming main sequence
is real and caused by variations in the star formation rate at fixed mass. At
high masses (10^10.5<M/Msun<10^11), above the main sequence, Ha is particularly
enhanced in the center, plausibly building bulges and/or supermassive black
holes. Below the main sequence, the star forming disks are more compact and a
strong central dip in the EW(Ha), and the inferred specific star formation
rate, appears. Importantly though, across the entirety of the SFR-M plane, the
absolute star formation rate as traced by Ha is always centrally peaked, even
in galaxies below the main sequence.
