2geom.pc pkg-config should "Requires" Boost
When using lib2geom as a library, Boost needs to be installed, as it is referenced by 2geom's own headers, such as can be seen here, when attempting to compile libdepixelize (used by Inkscape, available at: https://launchpad.net/libdepixelize).
[ 25%] Building CXX object src/CMakeFiles/depixelize.dir/kopftracer2011.cpp.o
cd /tmp/guix-build-libdepixelize-0.0.0-1.187.drv-0/build/src && /gnu/store/jmd83ck5v5abpmyasq0d1fzfhkz9qwaq-gcc-7.5.0/bin/c++ -I/gnu/store/fybhi8qfs3xzrs92mxgzgf3pshwrm105-gtkmm-2.24.5/include/gdkmm-2.4 -I/gnu/store/fybhi8qfs3xzrs92mxgzgf3pshwrm105-gtkmm-2.24.5/lib/gdkmm-2.4/include -I/gnu/store/sz1crisw8aszady08ba5wg56h90kz2mi-glibmm-2.62.0/include/giomm-2.4 -I/gnu/store/sz1crisw8aszady08ba5wg56h90kz2mi-glibmm-2.62.0/lib/giomm-2.4/include -I/gnu/store/sz1crisw8aszady08ba5wg56h90kz2mi-glibmm-2.62.0/include/glibmm-2.4 -I/gnu/store/sz1crisw8aszady08ba5wg56h90kz2mi-glibmm-2.62.0/lib/glibmm-2.4/include -I/gnu/store/sd6a2dkshcjb6gqvz6j9mr2r5wkdrib2-gtk+-2.24.32/include/gtk-2.0 -I/gnu/store/sd6a2dkshcjb6gqvz6j9mr2r5wkdrib2-gtk+-2.24.32/lib/gtk-2.0/include -I/gnu/store/380anx615dwy0s47p7h99miw7zliickq-cairomm-1.12.2/include/cairomm-1.0 -I/gnu/store/380anx615dwy0s47p7h99miw7zliickq-cairomm-1.12.2/lib/cairomm-1.0/include -I/gnu/store/0ma180yrwhidb1nx378aqzj2f9l28kk2-pangomm-2.42.0/include/pangomm-1.4 -I/gnu/store/0ma180yrwhidb1nx378aqzj2f9l28kk2-pangomm-2.42.0/lib/pangomm-1.4/include -I/gnu/store/ni89pvjhxwzgdzrlvw0rdfcm1l38whd5-glib-2.62.4/include/glib-2.0 -I/gnu/store/ni89pvjhxwzgdzrlvw0rdfcm1l38whd5-glib-2.62.4/lib/glib-2.0/include -I/gnu/store/hg2jxfbcg024p3b7ssx0yxr97r7mipcb-libsigc++-2.10.2/include/sigc++-2.0 -I/gnu/store/hg2jxfbcg024p3b7ssx0yxr97r7mipcb-libsigc++-2.10.2/lib/sigc++-2.0/include -I/gnu/store/dhr4mb3srs27y45dvy9qjd48vcmznx1r-pango-1.44.7/include/pango-1.0 -I/gnu/store/ifj4q56bykjz2qdijbm7bpcm1jvk77ai-gdk-pixbuf+svg-2.40.0/include/gdk-pixbuf-2.0 -I/gnu/store/nqwg2l4ncqpl50q4zxlhym4r7naika94-atk-2.34.1/include/atk-1.0 -I/gnu/store/3pq2xj838m2iywhg7kx2rxyara2q25b5-cairo-1.16.0/include/cairo -I/gnu/store/r1lhzxs4gf8k4y0y4fvl3yp3krx270cs-freetype-2.10.1/include/freetype2 -I/gnu/store/phh250vx8dy08gkxxmfwhdq49skfznkg-util-linux-2.35-lib/include/libmount -I/gnu/store/phh250vx8dy08gkxxmfwhdq49skfznkg-util-linux-2.35-lib/include/blkid -I/gnu/store/phh250vx8dy08gkxxmfwhdq49skfznkg-util-linux-2.35-lib/include/uuid -I/gnu/store/4dbs1740hsfhrl1nsmaaiwn5izqpj9m2-harfbuzz-2.6.4/include/harfbuzz -I/gnu/store/mp7irwq2jazvb7s0lp7q01cbc9z6g1c9-fribidi-1.0.8/include/fribidi -I/gnu/store/85s0a8f6ssdva9vk89vbhws2afgrj5bh-libpng-1.6.37/include/libpng16 -I/gnu/store/q3i6388271zjrnn34yvq48hrxhiaqf3j-pixman-0.38.4/include/pixman-1 -I/gnu/store/k0w998w6yxbp7pfzkki68whsflw2s4r1-lib2geom-1.0-1.5eb3544/include/2geom-1.0.0 -O2 -g -DNDEBUG -Wall -Wextra -Wsequence-point -Wnarrowing -o CMakeFiles/depixelize.dir/kopftracer2011.cpp.o -c /tmp/guix-build-libdepixelize-0.0.0-1.187.drv-0/source/src/kopftracer2011.cpp
In file included from /tmp/guix-build-libdepixelize-0.0.0-1.187.drv-0/source/src/splines.h:28:0,
from /tmp/guix-build-libdepixelize-0.0.0-1.187.drv-0/source/src/kopftracer2011.h:37,
from /tmp/guix-build-libdepixelize-0.0.0-1.187.drv-0/source/src/kopftracer2011.cpp:29:
/gnu/store/k0w998w6yxbp7pfzkki68whsflw2s4r1-lib2geom-1.0-1.5eb3544/include/2geom-1.0.0/2geom/pathvector.h:37:10: fatal error: boost/concept/requires.hpp: No such file or directory
#include <boost/concept/requires.hpp>
^~~~~~~~~~~~~~~~~~~~~~~~~~~~
compilation terminated.
I think this means that the 2geom.pc file should have Boost listed in a Requires field.