GoでJsonファイルを読み込んで構造体として扱う。

Json

sample.json

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "properties": {
        "pref": "富山県",
        "city1": "下新川郡",
        "city2": "朝日町"
      },
      "geometry": {
        "type": "Polygon",
        "coordinates": [
          [
            [
              136.111111,
              36.111111
            ],
            [
              136.222222,
              36.222222
            ]
          ]
        ]
      }
    },
    {
      "type": "Feature",
      "properties": {
        "pref": "富山県",
        "city1": "氷見市",
        "city2": ""
      },
      "geometry": {
        "type": "Polygon",
        "coordinates": [
          [
            [
              136.333333,
              36.333333
            ],
            [
              136.444444,
              36.444444
            ]
          ]
        ]
      }
    },
    {
      "type": "Feature",
      "properties": {
        "pref": "富山県",
        "city1": "高岡市",
        "city2": ""
      },
      "geometry": {
        "type": "Polygon",
        "coordinates": [
          [
            [
              136.555555,
              36.555555
            ],
            [
              138.666666,
              36.666666
            ]
          ]
        ]
      }
    }
  ]
}

Jsonと対になる構造体を用意したGo

main.go

package main

import (
    "encoding/json"
    "fmt"
    "io/ioutil"
    "os"
)

type FeatureCollection struct {
    Type     string    `json:"type"`
    Features []Feature `json:"features"`
}

type Feature struct {
    Type       string     `json:"type"`
    Properties Properties `json:"properties"`
    Geometory  Geometry   `json:"geometry"`
}

type Properties struct {
    Pref  string `json:"pref"`
    City1 string `json:"city1"`
    City2 string `json:"city2"`
}

type Geometry struct {
    Type        string     `json:"type"`
    Coordinates [][]LatLng `json:"coordinates"`
}

type LatLng [2]float64

func main() {

    raw, err := ioutil.ReadFile("./sample.json")
    if err != nil {
        fmt.Println(err.Error())
        os.Exit(1)
    }

    var fc FeatureCollection

    json.Unmarshal(raw, &fc)

    for _, ft := range fc.Features {
        fmt.Println(ft.Type)
        fmt.Println(ft.Properties.Pref, ft.Properties.City1, ft.Properties.City2)
        fmt.Println(ft.Geometory.Type)
        fmt.Println(ft.Geometory.Coordinates[0][0][0], ft.Geometory.Coordinates[0][0][1])
    }
}

実行結果

go run main.go
Feature
富山県 下新川郡 朝日町
Polygon
136.111111 36.111111
Feature
富山県 氷見市 
Polygon
136.333333 36.333333
Feature
富山県 高岡市 
Polygon
136.555555 36.555555