3D experiments are generally based upon 2D experiments and so the easiest way to think of a 3D is of a 2D which is then extended into a third dimension. Take, for instance, an HNCO. It is based upon a 2D HSQC (a), so the x and y axes are ^{1}H and ^{15}N, respectively. This is now extended into a third dimension which is a ^{13}C dimension. So the HSQC peaks will now not just lie in one plane, but they will be lifted up into the third dimension and lie at the ^{13}C ppm value of the CO group preceeding the NH group (b and c).

It is now possible to look at the 3D spectrum from various different angles and each time see a different plane. The ^{1}H dimension is generally left in the x-dimension and in most cases the ^{13}C dimension is viewed along the y-axis, leaving ^{15}N to form the z-plane. So essentially you end up looking at a ^{1}H-^{13}C 2D spectrum at varying places along the ^{15}N dimension (d and e).

Most spectra used for triple resonance backbone assignment have a ^{1}H, ^{15}N and ^{13}C dimension each. Several other types of spectra, most notably 3D NOESY spectra and HCCH-TOCSY/COSY spectra have two ^{1}H dimensions and one ^{15}N or ^{13}C dimension. In this case, the two ^{1}H dimensions are viewed in x and y and the ^{15}N or ^{13}C is left in the z-plane.

A common way of visualising 3D spectra is as so-called **Strips**. Consider, for instance, a particular z-plane of a 3D HNCO spectrum (a or b): you will probably end up with only one peak in that z-plane. (Even if there are peaks with a similar ^{15}N ppm value, they will lie just above or just below the actual plane you are currently looking at.) Therefore there is not much point in looking at the complete ^{1}H width of the spectrum and instead you can trim the area you look at to the ^{1}H region just surrounding your peak (c and d). This way you end up with a **Strip**. It corresponds to a particular ^{1}H and ^{15}N part of the spectrum, but shows the complete ^{13}C width. Thus, if you start with an HSQC where each peak is defined by a ^{1}H and ^{15}N value, you can then pick out strips for each HSQC peak and then lay them next to one another for easy comparison (e). For protein backbone assignment this is particularly useful.