# Lines on Maps in JavaScript

How to draw D3.js-based lines, great circles, and contours on maps in JavaScript. Lines on maps can show distance between geographic points or be contour lines (isolines, isopleths, or isarithms).

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### Lines on an Orthographic Map

d3.csv('https://raw.githubusercontent.com/plotly/datasets/master/globe_contours.csv', function(err, rows){

function unpack(rows, key) {
return rows.map(function(row) { return row[key]; });
}

var data = [];
var scl =['rgb(213,62,79)','rgb(244,109,67)','rgb(253,174,97)','rgb(254,224,139)','rgb(255,255,191)','rgb(230,245,152)','rgb(171,221,164)','rgb(102,194,165)','rgb(50,136,189)'];
var allLats = [];
var allLons = [];

for ( var i = 0 ; i < scl.length; i++){
var latHead = 'lat-'+i;
var lonHead = 'lon-'+i;
var lat = unpack(rows, latHead);
var lon = unpack(rows, lonHead);
allLats.push(lat);
allLons.push(lon);
}

for ( var i = 0 ; i < scl.length; i++) {
var current = {
type:'scattergeo',
lon: allLons[i],
lat: allLats[i],
mode: 'lines',
line: {
width: 2,
color: scl[i]
}
}
data.push(current);
};

var layout = {
geo: {
projection: {
type: 'orthographic',
rotation: {
lon: -100,
lat: 40
},
},
showocean: true,
oceancolor: 'rgb(0, 255, 255)',
showland: true,
landcolor: 'rgb(230, 145, 56)',
showlakes: true,
lakecolor: 'rgb(0, 255, 255)',
showcountries: true,
lonaxis: {
showgrid: true,
gridcolor: 'rgb(102, 102, 102)'
},
lataxis: {
showgrid: true,
gridcolor: 'rgb(102, 102, 102)'
}
}
};

Plotly.newPlot("myDiv", data, layout, {showLink: false});
});


### London to NYC Great Circle

var data = [{
type: 'scattergeo',
lat: [ 40.7127, 51.5072 ],
lon: [ -74.0059, 0.1275 ],
mode: 'lines',
line:{
width: 2,
color: 'blue'
}
}];

var layout = {
title: 'London to NYC Great Circle',
showlegend: false,
geo: {
resolution: 50,
showland: true,
showlakes: true,
landcolor: 'rgb(204, 204, 204)',
countrycolor: 'rgb(204, 204, 204)',
lakecolor: 'rgb(255, 255, 255)',
projection: {
type: 'equirectangular'
},
coastlinewidth: 2,
lataxis: {
range: [ 20, 60 ],
showgrid: true,
tickmode: 'linear',
dtick: 10
},
lonaxis:{
range: [-100, 20],
showgrid: true,
tickmode: 'linear',
dtick: 20
}
}
};

Plotly.newPlot('myDiv', data, layout);



### US Flight Paths Map

d3.csv('https://raw.githubusercontent.com/plotly/datasets/c34aaa0b1b3cddad335173cb7bc0181897201ee6/2011_february_aa_flight_paths.csv', function(err, rows){
function unpack(rows, key) {
return rows.map(function(row) { return row[key]; });}

function getMaxOfArray(numArray) {
return Math.max.apply(null, numArray);
}

var data = [];
var count = unpack(rows, 'cnt');
var startLongitude = unpack(rows, 'start_lon');
var endLongitude = unpack(rows, 'end_lon');
var startLat = unpack(rows, 'start_lat');
var endLat = unpack(rows, 'end_lat');

for ( var i = 0 ; i < count.length; i++ ) {
var opacityValue = count[i]/getMaxOfArray(count);

var result = {
type: 'scattergeo',
locationmode: 'USA-states',
lon: [ startLongitude[i] , endLongitude[i] ],
lat: [ startLat[i] , endLat[i] ],
mode: 'lines',
line: {
width: 1,
color: 'red'
},
opacity: opacityValue
};

data.push(result);
};

var layout = {
title: 'Feb. 2011 American Airline flight paths',
showlegend: false,
geo:{
scope: 'north america',
projection: {
type: 'azimuthal equal area'
},
showland: true,
landcolor: 'rgb(243,243,243)',
countrycolor: 'rgb(204,204,204)'
}
};

Plotly.newPlot("myDiv", data, layout, {showLink: false});

});