Zoomable World Map Example
A world map that pans and zooms in response to mouse drag and scroll wheel input. This example applies an inverse map projection (using Vega’s invert expression function) to map changes in pixel space to updated projection parameters.
Vega JSON Specification <>
{
"$schema": "https://vega.github.io/schema/vega/v5.json",
"description": "An interactive world map supporting pan and zoom.",
"width": 900,
"height": 500,
"autosize": "none",
"signals": [
{ "name": "tx", "update": "width / 2" },
{ "name": "ty", "update": "height / 2" },
{
"name": "scale",
"value": 150,
"on": [{
"events": {"type": "wheel", "consume": true},
"update": "clamp(scale * pow(1.0005, -event.deltaY * pow(16, event.deltaMode)), 150, 3000)"
}]
},
{
"name": "angles",
"value": [0, 0],
"on": [{
"events": "pointerdown",
"update": "[rotateX, centerY]"
}]
},
{
"name": "cloned",
"value": null,
"on": [{
"events": "pointerdown",
"update": "copy('projection')"
}]
},
{
"name": "start",
"value": null,
"on": [{
"events": "pointerdown",
"update": "invert(cloned, xy())"
}]
},
{
"name": "drag", "value": null,
"on": [{
"events": "[pointerdown, window:pointerup] > window:pointermove",
"update": "invert(cloned, xy())"
}]
},
{
"name": "delta", "value": null,
"on": [{
"events": {"signal": "drag"},
"update": "[drag[0] - start[0], start[1] - drag[1]]"
}]
},
{
"name": "rotateX", "value": 0,
"on": [{
"events": {"signal": "delta"},
"update": "angles[0] + delta[0]"
}]
},
{
"name": "centerY", "value": 0,
"on": [{
"events": {"signal": "delta"},
"update": "clamp(angles[1] + delta[1], -60, 60)"
}]
}
],
"projections": [
{
"name": "projection",
"type": "mercator",
"scale": {"signal": "scale"},
"rotate": [{"signal": "rotateX"}, 0, 0],
"center": [0, {"signal": "centerY"}],
"translate": [{"signal": "tx"}, {"signal": "ty"}]
}
],
"data": [
{
"name": "world",
"url": "data/world-110m.json",
"format": {
"type": "topojson",
"feature": "countries"
}
},
{
"name": "graticule",
"transform": [
{ "type": "graticule", "step": [15, 15] }
]
}
],
"marks": [
{
"type": "shape",
"from": {"data": "graticule"},
"encode": {
"enter": {
"strokeWidth": {"value": 1},
"stroke": {"value": "#ddd"},
"fill": {"value": null}
}
},
"transform": [
{ "type": "geoshape", "projection": "projection" }
]
},
{
"type": "shape",
"from": {"data": "world"},
"encode": {
"enter": {
"strokeWidth": {"value": 0.5},
"stroke": {"value": "#bbb"},
"fill": {"value": "#e5e8d3"}
}
},
"transform": [
{ "type": "geoshape", "projection": "projection" }
]
}
]
}