go-mapzen-js

Go middleware package for mapzen.js

Important

This package is no longer being maintained. You should use go-http-nextzenjs instead.

Install

You will need to have both Go (specifically a version of Go more recent than 1.6 so let's just assume you need Go 1.8 or higher) and the make programs installed on your computer. Assuming you do just type:

make bin

All of this package's dependencies are bundled with the code in the vendor directory.

A word about "Mapzen" and naming things

Mapzen is no more. As I write this I am not really sure what the state of nextzen.js (formerly mapzen.js) is. To top it off all the map vector tiles are now called Tilezen but are hosted under the Nextzen domain. The same is true of tangram.js.

It's a bit confusing but so is life.

So while this package bundles and exposes a copy of the old mapzen.js it won't work as you'd normally expect, like this:

	// remember this data attribute is squirted in to the source via
	// the MapzenJSHandler (.go) handler

	var body = document.body;
	var api_key = body.getAttribute("data-mapzen-api-key");

	L.Mapzen.apiKey = api_key;
			
	var map_opts = { tangramOptions: {
		scene: L.Mapzen.BasemapStyles.Refill
	}};
			
	map = L.Mapzen.map('map', map_opts);

Or at least I'm not sure it will, as I write this. Instead what I (currently) do is this:

	// remember this data attribute is squirted in to the source via
	// the MapzenJSHandler (.go) handler

	var body = document.body;
	var api_key = body.getAttribute("data-mapzen-api-key");

	var sources = {
	    mapzen: {
		url: 'https://{s}.tile.nextzen.org/tilezen/vector/v1/512/all/{z}/{x}/{y}.topojson',
		url_subdomains: ['a', 'b', 'c', 'd'],
		url_params: {
		    api_key: api_key	// not clear this actually works... ?
		},
		tile_size: 512,
		max_zoom: 15
	    }
	};
			
	var scene = {
	    import: [
		     "/tangram/refill-style.zip",
		     "/tangram/refill-style-themes-label.zip",
		     ],
	    sources: sources,
	    global: {
		sdk_mapzen_api_key: api_key,
	    },
	};
			
	var attributions = {
	    "Tangram": "https://github.com/tangrams/",
	    "© OSM contributors": "http://www.openstreetmap.org/",
	    "Who\"s On First": "http://www.whosonfirst.org/",
	    "Nextzen": "https://nextzen.org/",
	};
			
	var attrs = [];
			
	for (var label in attributions){
			    
	    var link = attrs[label];
			    
	    if (! link){
		attrs.push(label);
		continue;
	    }
			    
	    var anchor = '<a href="' + link + '" target="_blank">' + enc_label + '</a>';
	    attrs.push(anchor);
	}
			
	var str_attributions = attrs.join(" | ");
			
	// waiting for nextzen.js to be updated to do all the things - that said it's
	// not entirely clear we need all of (map/next)zen.js and could probably get
	// away with leaflet + tangram but for now we'll just keep on as-is...
	// (20180304/thisisaaronland)
			
	L.Mapzen.apiKey = api_key;
			
	var map_opts = {
	    tangramOptions: {
		scene: scene,
		attribution: attributions,
	    }
	};
	
	map = L.Mapzen.map('map', map_opts);

Which, you know, arguably could be wrapped in a helper function/library exposed by the MapzenJSAssetsHandler handler but presumably nextzen.js will (has been) updated to point to all the new Nextzen things, right?

To further confuse matters it's on my list to update this package to bundle and expose plain vanilla Leaflet support for Tangram and Tilezen stuff but that hasn't happened yet.

So maybe this package should be called go-http-nextzen... but it isn't... yet... probably.

We'll figure it out soon but honestly, it's kind of a wonder anyone figured out how to use our (Mapzen) stuff at all. Which is why everything in this package is still called "mapzen".

Handlers

MapzenJSHandler(http.Handler, MapzenJSOptions) (http.Handler, error)

This handler will optionally modify the output of the your_handler http.Handler as follows:

• Append the relevant mapzen.js script and link elements to the head element.
• Append a data-mapzen-api-key attribute (and value) to the body element.

import (
	"github.com/whosonfirst/go-http-mapzenjs"
	"net/http"
)

func main(){

	opts := mapzenjs.DefaultMapzenJSOptions()
	opts.APIKey = "mapzen-1a2b3c"

	www_handler := YourDefaultWWWHandler()
	
	mapzenjs_handler, _ := mapzenjs.MapzenJSHandler(www_handler, opts)

	mux := http.NewServeMux()
	mux.Handle("/", mapzenjs_handler)

Note that error handling has been removed for the sake of brevity.

MapzenJSOptions

The definition for MapzenJSOptions looks like this:

type MapzenJSOptions struct {
	AppendAPIKey bool
	AppendJS     bool
	AppendCSS    bool
	APIKey       string
	JS           []string
	CSS          []string
}

Default MapzenJSOptions are:

	opts := MapzenJSOptions{
		AppendAPIKey: true,
		AppendJS:     true,
		AppendCSS:    true,
		APIKey:       "mapzen-xxxxxx",
		JS:           []string{"/javascript/mapzen.min.js"},
		CSS:          []string{"/css/mapzen.js.css"},
	}

Example

Given the following markup generated by your http.Handler output:

<!DOCTYPE html>
<html lang="en">
  <head>
	  <title>Example</title>
	  <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
	  <meta name="referrer" content="origin">
	  <meta http-equiv="X-UA-Compatible" content="IE=9" />
	  <meta name="apple-mobile-web-app-capable" content="yes" />
	  <meta name="apple-mobile-web-app-status-bar-style" content="black" />
	  <meta name="HandheldFriendly" content="true" />
	  <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, minimum-scale=1, user-scalable=no" />
  </head>
  <body>
  <!-- and so on... ->

The MapzenJSHandler handler will modify that markup to return:

<!DOCTYPE html>
<html lang="en">
  <head>
	  <title>Example</title>
	  <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
	  <meta name="referrer" content="origin">
	  <meta http-equiv="X-UA-Compatible" content="IE=9" />
	  <meta name="apple-mobile-web-app-capable" content="yes" />
	  <meta name="apple-mobile-web-app-status-bar-style" content="black" />
	  <meta name="HandheldFriendly" content="true" />
	  <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, minimum-scale=1, user-scalable=no" />
	  <script type="text/javascript" src="/javascript/mapzen.min.js"></script>
	  <link rel="stylesheet" type="text/css" href="/css/mapzen.js.css" />
  </head>
  <body data-mapzen-api-key="mapzen-1a2b3c">
  <!-- and so on... ->

MapzenJSAssetsHandler() (http.Handler, error)

The handler will serve mapzen.js and tangram.js related assets which have been bundled with this package.

import (
	"github.com/whosonfirst/go-http-mapzenjs"
	"net/http"
)

func main(){

	mapzenjs_assets_handler, _ := mapzen.MapzenJSAssetsHandler()

	mux := http.NewServeMux()

	mux.Handle("/javascript/mapzen.js", mapzenjs_handler)
	mux.Handle("/javascript/mapzen.min.js", mapzenjs_handler)
	mux.Handle("/javascript/tangram.js", mapzenjs_handler)	
	mux.Handle("/javascript/tangram.min.js", mapzenjs_handler)
	mux.Handle("/css/mapzen.js.css", mapzenjs_handler)
	mux.Handle("/tangram/refill-style.zip", mapzenjs_handler)

}

You can update the various mapzen.js and tangram.js assets manually by invoking the build target in the included Makefile.

Styles

Currently the following styles are bundled with this package:

• refill
• walkabout

To do

• Add a tile caching proxy

See also

• https://mapzen.com/documentation/mapzen-js/
• https://github.com/tangrams/tangram