= Wing planform
A \b[wing planform] is the two-dimensional outline of an <aircraft wing> viewed from above. It is bounded by the projected <leading edge>, <trailing edge> and wing tips. A rectangular, tapered or swept <wing planform> can be combined with many different <airfoil> profiles; the outline alone does not specify the wing's thickness or <airfoil camber>.<Wing Geometry by NASA Glenn Research Center>[Top View and Airfoil Geometry]{ref}
Let $x$ point aft and $y$ run along the <wingspan>. Describe the two edges by $x_{\rm LE}(y)$ and $x_{\rm TE}(y)$. Their separation is the projected local <airfoil chord>,
$$
c(y)=x_{\rm TE}(y)-x_{\rm LE}(y),\qquad
S=\int_{-b/2}^{b/2}c(y)\,dy.
$$
The second equation computes <wing area>. The first retains information lost by that single area value: where the chord lies along the fore-and-aft direction.
For an original comparison, a rectangular wing with $b=10\,\mathrm{m}$ and $c=2\,\mathrm{m}$ has $S=20\,\mathrm{m^2}$. A symmetric trapezoidal wing of the same <wingspan>, root chord $3\,\mathrm{m}$ and tip chord $1\,\mathrm{m}$ also has $S=20\,\mathrm{m^2}$. Now shift both edges of each spanwise strip aft by $k|y|$: the local <airfoil chord> and <wing area> stay unchanged, while the <wing sweep> changes. This explains geometrically why even specifying <wingspan>, <wing area> and <wing taper ratio> does not uniquely determine a <wing planform>.
\Image[/wing-planform-equal-area.png]
{title=Three wing planforms with equal span and projected area}
The construction compares geometry, not aerodynamic equivalence. The <airfoil>, <angle of attack> and three-dimensional <fluid flow> still matter when predicting <lift> and <drag>.
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