What Lin calls "knowing the earth" involves becoming familiar with different geographical environments. High mountains, rivers and marine islands all have their different appearances and their own special types of plants and animals; tropical, temperate and frigid zones have their own natural conditions that cannot be confused.
所謂知地，指須熟知大地地理環境的不同，高山、河川、海島等各種不同的地貌上，都有特殊的動植物存在；熱帶、溫帶、寒帶間則有不容並論的自然條件。