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This process involves two main steps, namely terrain feature line extraction and contour bend selection. The terrain feature line extraction includes two steps, that is, terrain feature point extraction and classification, and terrain feature line connection. However, to date, many similar studies have not considered the hierarchy of terrain features. Therefore, we proposed a group simplification method for contour lines based on classified terrain features and tested it on a study area with mainly positive landforms. In accordance with geomorphological theory, we divided valleys into either gradually descending or ordinary. Valley points were extracted based on the constrained Delaunay triangulation method and then classified into the two categories. Gradually descending and ordinary valley lines were then connected. The contour bends were grouped based on the valley lines extracted and then selected according to the geometric indicators of the bend group. The results have demonstrated that the valley lines extracted closely matched human perception in integrity and structure. Contour lines simplified by our method achieved effective reduction of map information and adequate retention of the main terrain structures, which are similar to those from manual simplification.<\/jats:p>","DOI":"10.3390\/ijgi12020071","type":"journal-article","created":{"date-parts":[[2023,2,20]],"date-time":"2023-02-20T05:27:01Z","timestamp":1676870821000},"page":"71","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":3,"title":["A Contour Line Group Simplification Method Based on Classified Terrain Features"],"prefix":"10.3390","volume":"12","author":[{"given":"Yuanfu","family":"Li","sequence":"first","affiliation":[{"name":"Institute of Geospatial Information, PLA Strategic Support Force Information Engineering University, Zhengzhou 450052, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Qun","family":"Sun","sequence":"additional","affiliation":[{"name":"Institute of Geospatial Information, PLA Strategic Support Force Information Engineering University, Zhengzhou 450052, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Wenyue","family":"Guo","sequence":"additional","affiliation":[{"name":"Institute of Geospatial Information, PLA Strategic Support Force Information Engineering University, Zhengzhou 450052, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Qing","family":"Xu","sequence":"additional","affiliation":[{"name":"Institute of Geospatial Information, PLA Strategic Support Force Information Engineering University, Zhengzhou 450052, China"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Xinming","family":"Zhu","sequence":"additional","affiliation":[{"name":"Institute of Geospatial Information, PLA Strategic Support Force Information Engineering University, Zhengzhou 450052, China"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2023,2,18]]},"reference":[{"key":"ref_1","first-page":"1570","article-title":"Progress of digital terrain analysis on regional geomorphology in China","volume":"46","author":"Tang","year":"2017","journal-title":"Acta Geod. 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