One if the interesting topics in SharePoint customizations is developing customized list definitions to be integrated later on within you site definitions.During list definitions development you are required to determine two important values "Type" and "BaseType", following is a description for the available types (available in the WSS SDK)
Type:
Value Description
100 Generic list
101 Document library
102 Survey
103 Links list
104 Announcements list
105 Contacts list
106 Events list
107 Tasks list
108 Discussion board
109 Picture library
110 Data sources
111 Site template gallery
113 Web Part gallery
114 List template gallery
115 XML Form library
120 Custom grid for a list
200 Meeting Series list
201 Meeting Agenda list
202 Meeting Attendees list
204 Meeting Decisions list
207 Meeting Objectives list
210 Meeting text box
211 Meeting Things To Bring list
212 Meeting Workspace Pages list
300 Portal Sites list.
1100 Issue tracking
2002 Personal document library
2003 Private document library
BaseType
0 – Custom List
1 – Document Library
2 – Not used
3 – Discussion Forum
4 – Surveys
5 – Issues List
so, if you are developing custom picture library set Type="109" and BaseType="1" (because picture library mainly based on document library)
another example if your are developing custom Calendar list definition set Type="100" BaseType="0".
hope it is useful ciao 