Final answer:
In the context of mapping community capacity, Tertiary building blocks are the least accessible assets as they often require extensive external networking and influence.
Step-by-step explanation:
When mapping community capacity, the least accessible assets are typically considered to be Tertiary building blocks. These include the resources that are not immediately available within the community and often require broader networking, political influence, or extensive mobilization to utilize. Tertiary assets might encompass regional, national, or global resources, affiliations, or institutions that could potentially support the community's development, but they are not as readily accessible as Primary or Secondary building blocks, which are more closely integrated within the community's fabric.