August 2017
Intermediate to advanced
500 pages
12h 3m
Japanese
Content preview from PythonとJavaScriptではじめるデータビジュアライゼーション
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394
18 章 D3 を使った地図の作成
"type": "Feature",
"id": "ZWE",
"properties": {
"name": "Zimbabwe"
},
"geometry": {
"type": "Polygon",
"coordinates": [
[
[...
}
}
]
}
❶
GeoJSON
ファイルには型を持つ
1
つのオブジェクトと、
❷
Feature
の配列（この場合は国オブジェクト）が含まれ、
❸ 座標ベースのポリゴン形状を持つ。
❹ 地理座標は［経度，
緯度］のペアで指定し、従来の地理位置指定と逆。
GeoJSON
は
[X, Y]
座標スキーム
を使うからである。
GeoJSON
の方がシェープファイルよりも簡潔であり望ましい
JSON
フォーマットですが、地図
のエンコーデイングに多くの冗長性があります。例えば、共有境界を
2
回指定し、浮動小数点数
座標フォーマットはあまり柔軟性がなく、大抵は細かすぎます。
TopoJSON
フォーマットはこの
ような課題を解決するように設計されており、効率的に地図をブラウザに配信できます。
18.2.2
TopoJSON
Mike Bostock
が開発した
TopoJSON
は位相をエンコードする
GeoJSON
の拡張で、弧（アー
ク、
arc
）と呼ばれる線分の共有プールからジオメトリ（幾何形状）をつなぎ合わせます。この弧
を再利用するため、
TopoJSON
ファイルは同等の
GeoJSON
よりも一般に
80 %
小さくなります。
さらに、地図表現に位相幾何学的アプローチをとるため、位相幾何学を使ったさまざまなテクニッ ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.