Laws, in expressing the relationships that existed in the world, are powerful ways for people to understand and communicate human understandings. In this paper through the comparison of laws in geography and those well accepted laws in physics (namely Newton's Laws), we concluded that the laws in geography also fit the definition of "law" albeit the laws in geography are different from the laws in physics in how they are generated and how they are expressed. We further compared the geographic similarity principle or the Third Law of Geography as suggested by Zhu et al (Annals of GIS, 2018,24(4):225-240) with the existing laws of geography from the perspectives of broadness, independence and applicability and found that the geographic similarity principle has the similar broad implications in geography as the other two laws but it is fundamentally different from the other two. It solves problems in geographic analysis that the other two were found to be insufficient. We thus believe that geographic similarity principle would serve a great candidate of the Third Law of Geography.