我只讲意思相近的解释.
frontier - 未开拓领域的边界线,示意未开发的疆土.
border - 两区或两国之间的界线,即：边界.
boundary - 有限制性意义的界线,延伸为边界线.字根是bound,围绕的意思.
金山词霸中的参考资料：
boundary, border, frontier, limit
These nouns all denote a line or an area separating one piece of territory from another. A
所有这些名词都指分隔一地域与另一地域的线或地区.
boundary is a limiting line:
boundary 是限制线：
A stone wall marked the boundary between the two farms. A
石墙是两个农场的分界线.
border is a line that separates political entities:
Border 是将政治实体分离的界限：
Customs officers inspected our luggage when we crossed the border.
当我们过境时海关官员检查了我们的行李.
Frontier denotes the part of a country that faces toward or fronts an adjoining country:
Frontier 意指一国中朝向或面对邻国的部分：
“that long [Canadian] frontier from the Atlantic to the Pacific Oceans, guarded only by neighborly respect and honorable obligations” (Winston S. Churchill).
“那条 自大西洋至太平洋的长边界线, 仅出于邻国的尊敬和高尚义务守护着” （温斯顿·S·丘吉尔）.
Limit denotes a boundary that surrounds an area:
Limit 意指包围一地区的界线：
Cars cannot exceed 35 miles per hour within city limits.
在市区线以内车速不能超过每小时35英里