  Localization estimates for GW150914, the first binary black hole detected by
the LIGO instruments, were shared with partner facilities for electromagnetic
follow-up. While the source was a compact binary coalescence (CBC), it was
first identified by algorithms that search for unmodeled signals, which
produced the skymaps that directed electromagnetic observations. Later on, CBC
specific algorithms produced refined versions, which showed significant
differences. In this paper we show that those differences were not accidental
and that CBC and unmodeled skymaps for binary black holes will frequently be
different; we thus provide a way to determine whether to observe
electromagnetically as promptly as possible (following a gravitational-wave
detection), or to wait until CBC skymaps become available, should they not be
available in low latency. We also show that, unsurprisingly, CBC algorithms can
yield much smaller searched areas.
