目标

获取一个最简单的OSM文件，并学习其最基础的结构。

获取OSM数据的步骤

操作很简单：
进入官网：https://www.openstreetmap.org/
点击左上角的 “导出” 按钮。
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然后，填入坐标范围，点击按钮即可导出osm文件：

当然，直接填坐标范围是不直观的，为此，可以点击 “手动选择不同的区域”，这样即可手动选择范围了：

学习OSM文件格式的最基础结构

Wiki上有关于OSM格式的简单介绍，可见附录。不过这里将通过例子来学习：

例1：最简单的例子

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导出后的osm文件内容如下：

<?xml version="1.0" encoding="UTF-8"?>
<osm version="0.6" generator="CGImap 0.8.8 (2798843 spike-07.openstreetmap.org)" copyright="OpenStreetMap and contributors" attribution="http://www.openstreetmap.org/copyright" license="http://opendatacommons.org/licenses/odbl/1-0/">
 <bounds minlat="31.3618700" minlon="121.8012200" maxlat="31.3620700" maxlon="121.8015200"/>
 <node id="7603536329" visible="true" version="1" changeset="86368470" timestamp="2020-06-08T19:00:07Z" user="Reboot01" uid="9856191" lat="31.3618772" lon="121.8012886"/>
 <node id="7603536330" visible="true" version="1" changeset="86368470" timestamp="2020-06-08T19:00:07Z" user="Reboot01" uid="9856191" lat="31.3619399" lon="121.8014870"/>
 <node id="7603536331" visible="true" version="1" changeset="86368470" timestamp="2020-06-08T19:00:07Z" user="Reboot01" uid="9856191" lat="31.3620542" lon="121.8014375"/>
 <node id="7603536332" visible="true" version="1" changeset="86368470" timestamp="2020-06-08T19:00:07Z" user="Reboot01" uid="9856191" lat="31.3619915" lon="121.8012390"/>
 <way id="813970381" visible="true" version="1" changeset="86368470" timestamp="2020-06-08T19:00:07Z" user="Reboot01" uid="9856191">
  <nd ref="7603536329"/>
  <nd ref="7603536330"/>
  <nd ref="7603536331"/>
  <nd ref="7603536332"/>
  <nd ref="7603536329"/>
  <tag k="building" v="yes"/>
 </way>
</osm>

可以看到有以下信息：

经度(longitude)和纬度(latitude)缩写为lon和lat
bounds节点记录了这个文件的范围
4个node节点代表了4个位置。
way节点引用了node节点（通过id），以这样的方式表示出了一个范围。以此可见way节点并不仅表示“路(way)”。
tag指出了这个way节点是一个建筑(building)

例2：不同的way

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这里就出现了多个way节点，并且根据tag可以区分出各自的种类：

比如这里不仅有建筑，还有操场，和跑道。

例3：relation的一个例子

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这是横沙岛的一个边界。可以在文件中找到一个relation节点，它指明了自己的边界包含了哪些way节点：

总结

结合这些简单的例子，以及Wiki的介绍，我学到关于OSM文件的一些最基础的结构：

每个node节点代表空间中的一个位置，具有经纬度属性。
way节点引用了node，以有序列表的方式定义了一个范围。
relation节点(关系)引用了way节点（wiki指出还可能引用node或其他relation）作为成员（member），并且指出了每个成员在这个关系中所扮演的角色。
每个节点都可能包含tag属性，来附带上额外的信息。

附录：Wiki上关于OSM格式的介绍

Wiki地址：https://en.wikipedia.org/wiki/OpenStreetMap

OpenStreetMap uses a topological data structure, with four core elements (also known as data primitives):

Nodes are points with a geographic position, stored as coordinates (pairs of a latitude and a longitude) according to WGS 84.^[106] Outside of their usage in ways, they are used to represent map features without a size, such as points of interest or mountain peaks.
Ways are ordered lists of nodes, representing a polyline, or possibly a polygon if they form a closed loop. They are used both for representing linear features such as streets and rivers, and areas, like forests, parks, parking areas and lakes.
Relations are ordered lists of nodes, ways and relations (together called "members"), where each member can optionally have a "role" (a string). Relations are used for representing the relationship of existing nodes and ways. Examples include turn restrictions on roads, routes that span several existing ways (for instance, a long-distance motorway), and areas with holes.
Tags are key-value pairs (both arbitrary strings). They are used to store metadata about the map objects (such as their type, their name and their physical properties). Tags are not free-standing, but are always attached to an object: to a node, a way or a relation. A recommended ontology of map features (the meaning of tags) is maintained on a wiki. New tagging schemes can always be proposed by a popular vote of a written proposal in OpenStreetMap wiki, however, there is no requirement to follow this process. There are over 89 million different kinds of tags in use as of June 2017.^[107]

简单学习OSM（OpenStreetMap）文件格式的最基础结构

目标