How are lead fields mapped to other fields during conversion?

When you convert a lead, data in standard lead fields is transferred into standard account, contact, and opportunity fields. For custom lead fields, the data is mapped to custom account, contact, and opportunity fields as specified by your admin.

Any standard lead picklist fields that are blank inherit the default picklist value for accounts, contacts, and opportunities. If you use record types, all records created during lead conversion adopt the default record type for the owner of the newly created account, contact, and opportunity.