What is the meaning of Square and Triangle boxes in Census Enumeration lists?

A square means a pucca house. A triangle means a kuccha house as follows.

This time, the census enumerators went from house to house to collect data about each household and were asked to obtain the signature or thumb impression (in the case of illiterate respondents) of the head of the household on the census questionnaire. This was an important step towards improving the quality of data in the 2011 Census. A literate head of the household was given an opportunity to go through what the enumerator has written about his household members. He was ­expected to correct any wrong entry.

The census questionnaire was published in 18 Indian regional languages. The census enumerator carried with him not only the questionnaire in English but also in the relevant regional language.