We determine the physical conditions in NGC 6543, obtaining two different estimates of the electron temperature (T[e]) and one estimate of the electron density (N[e]). The electron temperature is computed by means of the [O III] ratio lambda 5007/ lambda 4363, and of the diagnostic diagram combining lambda 5007 to the [O III] infrared lines 52 mu and 88 mu . The continuum intensity measured on slit spectra is much higher than theoretically predicted under the simplest assumptions. After considering several possibilities, we suggest enhanced 2-photon emission as the most probable source of the additional continuum. While T[e] and N[e] derived from the diagnostic diagram agree with the most recent determination, T[e] derived from lambda 5007/ lambda 4363 is smaller than previously published values, probably due to the bias in lambda 4363 introduced by the uncertainty in the continuum. Our main conclusion is that it is not possible, with present-day data, to derive accurate temperature maps of photoionized nebulae.