OpenLayer4——GeoJSON简介

GeoJSON实际上就是一个JSON，为了满足GIS编程需要，额外定制了这样一套规则。
geojson中包含了点、线、面的数据，包含大量的坐标的数组

（不需要过分深入研究，如果参与GIS编程，短时间内就会接触大量这样的数据）

gsojson样例1

独立的feature

{"type":"Feature",
    "properties":{},
    "geometry":{
        "type":"Point",
        "coordinates":[105.380859375,31.57853542647338]
    }
}

gsojson样例2

feature集合

{
    "type": "FeatureCollection",
    "features": [{
            "type": "Feature",
            "geometry": {
                "type": "Point",
                "coordinates": [102.0, 0.5]
            },
            "properties": {
                "prop0": "value0"
            }
        }, {
            "type": "Feature",
            "geometry": {
                "type": "LineString",
                "coordinates": [[102.0, 0.0], [103.0, 1.0], [104.0, 0.0], [105.0, 1.0]]
            },
            "properties": {
                "prop0": "value0",
                "prop1": 0.0
            }
        }
    ]
}

GeoJSON成员变量

完整的GeoJSON，最外层往往是Feature或者FeatureCollection，Feature包含一个或多个Geometry，Geometry下面则是具体的几何数据（坐标数组和数据类型）。

GeoJSON

type：值必须是这些值其中一个："Point","MultiPoint","LineString", "MultiLineString", "Polygon","MultiPolygon","GeometryCollection","Feature" 或者 "FeatureCollection”。

properties：携带参数，用于辅助图形绘制，并没有内容限制。(常见的比如：图形的名称、地图的样式)。

Geometry（几何图形，点、线、面图形数据）

Type：图形类型，分为Point、MultiPoint、LineString、MultiLineString、Polygon、MultiPolygon、GeometryCollection。

Coordinates：地图坐标数组

英文介绍

The GeoJSON object may have any number of members (name/value pairs).

The GeoJSON object must have a member with the name "type". This member's

value is a string that determines the type of the GeoJSON object.

The value of the type member must be one of: "Point", "MultiPoint",

"LineString", "MultiLineString", "Polygon", "MultiPolygon",

"GeometryCollection", "Feature", or "FeatureCollection". The case of the type

member values must be as shown here.

A GeoJSON object may have an optional "crs" member, the value of which must

be a coordinate reference system object .

A GeoJSON object may have a "bbox" member, the value of which must be a

bounding box array.

A geometry is a GeoJSON object where the type member's value is one of the

following strings: "Point", "MultiPoint", "LineString", "MultiLineString",

"Polygon", "MultiPolygon", or "GeometryCollection".

A GeoJSON geometry object of any type other than "GeometryCollection" must have

a member with the name "coordinates". The value of the coordinates member is

always an array. The structure for the elements in this array is determined by

the type of geometry.