To DoctorJeff: I'm glad you express the importance of dwarf planets in terms of "surface to be explored" (or mapped, or studied or mined or colonized, whatsoever). Indeed most too often people think of them in terms of diameter and compare them to countries on Earth. by doing so they are comparing carrots with apples. Instead they should take the area into consideration.
I had recently updated a table giving a rough equivalence between the largest TNOs and continents/countries on Earth area-wise.
For the 15 largest TNOs (diameters are rough estimates, given the large dispersion on TNO's albedos, so who is in the top-15 list is debatable, no matter) that gives:
TNO / Diameter / Area in km2 / Area roughly equivalent to
Eris / 2400 / 18095573,68 / USA + Canada
Pluto / 2315 / 16836501,89 / Russia
Makemake 1700 9079202,77 China
Sedna 1550 7547676,35 Australia
Haumea 1400 6157521,6 Europe [excl. Russia]
Charon 1206 4569245,45 1st half of Brazil
Quaoar 1150 4154756,28 2nd half of Brazil
2007OR10 1100 3801327,11 Egypt+Sudan
2002 TC302 1000 3141592,65 India
Orcus 950 2835287,37 Argentina
2005QU182 850 2269800,69 Congo
Varuna 840 2216707,78 Algeria
2002 UX25 800 2010619,3 Saudi Arabia
2002 AW197 790 1960667,98 Mexico
Ixion 760 1814583,92 Indonesia
That is a total of almost 90 millions sq km, more than half of Earth's land mass. And only for the 15 largest known to day...
Best regards.