  We test the efficacy of the energy-balance spectral energy distribution (SED)
fitting code Magphys for recovering the spatially-resolved properties of a
simulated isolated disc galaxy, for which it was not designed. We perform
226,950 Magphys SED fits to regions between 0.2kpc and 25kpc in size across the
galaxy's disc, viewed from three different sight-lines, to probe how well
Magphys can recover key galaxy properties based on 21 bands of UV--far-infrared
model photometry. Magphys yields statistically acceptable fits to $> 99$ per
cent of the pixels within the $r$-band effective radius and between 59 and 77
per cent of pixels within 20kpc of the nucleus. Magphys is able to recover the
distribution of stellar mass, star formation rate (SFR), specific SFR, dust
luminosity, dust mass, and $V$-band attenuation reasonably well, especially
when the pixel size is $> \sim1$ kpc, whereas non-standard outputs (stellar
metallicity and mass-weighted age) are recovered less well. Accurate recovery
is more challenging in the smallest sub-regions of the disc (pixel scale $<
\sim 1$ kpc), where the energy balance criterion becomes increasingly
incorrect. Estimating integrated galaxy properties by summing the recovered
pixel values, the true integrated values of all parameters considered except
metallicity and age are well recovered at all spatial resolutions, ranging from
0.2kpc to integrating across the disc, albeit with some evidence for
resolution-dependent biases. These results must be considered when attempting
to analyse the structure of real galaxies with actual observational data, for
which the `ground truth' is unknown.
