Every House of Worship has nine sides... The number nine has a significance for Baha'is as it symbolizes the name of "Baha" in the Abjad reckoning.
Years ago Abdul-Baha spoke of the first House of Worship built in Ishqabad (Today in Turkministan):
"The Mashriqu'l-Adhkar in Ishqabad is almost completed. It is centrally located, nine avenues leading into it, nine gardens, nine fountains; all the arrangement and construction is according to the principle and proportion of the number nine. It is like a beautiful bouquet. Imagine a very lofty, imposing edifice surrounded completely by gardens of variegated flowers, with nine avenues leading through them, nine fountains and pools of water."
~ Abdu'l-Baha, The Promulgation of Universal Peace, p. 71
Ideally each House of Worship should have auxiliary institutions providing education, health and social services for the communities they serve surrounding the House of Worship.
Because resources were limited it was decided to start with a House of worship for each continent but eventually we hope that thousands will be erected...
"Thousands of Mashriqu'l-Adhkars, dawning points of praise and mention of God for all religionists will be built in the East and in the West..."
~ Abdu'l-Baha, The Promulgation of Universal Peace, p. 71
The Arabic name for a House of Worship is "Mashriqu'l-Adhkar" which translated means: "Dawning place for the mention of God".