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. 2020 Apr 15;20:483. doi: 10.1186/s12889-020-8314-8

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© The Author(s). 2020

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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Fig. 1 — The study area in map of China. (This map is downloaded from the standard map website of the Chinese government and can be used directly. And standard map website: http://bzdt.ch.mnr.gov.cn/browse.html?picId=“4o28b0625501ad13015501ad2bfc0292”. Permissions: The public can browse and download the standard map free of charge from the standard map website, and need to mark the map content approval number when using the standard map directly. The map content approval number we used in this paper is GS (2019)1675, as shown in the figure)