Hello.

In Arfken(6rd edi.), p.104 around eqn(2.3),

~~In general, these unit vectors will depend on the position in space. Then a vector may be written,
$$V=\hat {q_{1}}V_{1}+ \hat q_{2} V_{2}+ \hat q_{3} V_{3}$$
$$\underline{\mbox{but the coordinate or position vector is different in general,}}\\ r \neq \hat q_{1} V_{1}+ \hat q_{2} V_{2}+ \hat q_{3} V_{3} ,$$
$$\mbox{as the special case}$$
$$r=r\hat r \\\\\\\ \mbox{for spherical polar coordinates and}\\\\\\\\ r= \rho \hat \rho +z \hat z \\\\\\\\\\ \mbox {for cylindrical coordinates demonstrate. \cdots}$$
What's the meaning of the underlined sentence?

tiny-tim