Original subtitles

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Hi, welcome again and in this lecture I'll

show you how to add another layer to

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this map. Currently we have two layers we

have the base map which are map tiles by

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map box you can see here and the data

are served by Open Street Map and you

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also have your custom layer as well

which is a layer containing circle

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markers. So in GIS, geographic information

systems these are referred to as layers.

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Now I'd like to add a third layer to my

map and that will be a polygon layer.

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So this current layer with markers, this

can be referred to as a point layer.

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You also have line layers and polygon

layers so with points, points are better

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to represent locations and you have

lines, lines are best for representing

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geographical features which resembles

lines such as roads and rivers and then

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we have polygons. Polygons are best to

represent areas so for instance in this

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lecture what I'll show you is how to add

a layer, a polygon layer that represents

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world population by country, so countries

are represented as areas and what we're

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going to do is each of the countries

will have a specific color which will

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indicate the population of that country

so points for locations lines, for lines,

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and polygons for areas. Now of course you

need to have some data to create

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a polygon layer. You know just like as we

did with markers we had some data in CSV

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in text format and then we used those

data, we opened them with Pandas and then

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we iterated through those lines of

data and we added the markers to the map.

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Now for polygons the way to add

polygons via Folium is by

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using the folium.GeoJson method,

so basically let me make some space here

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the way this would work is you want to

add to feature group the variable here.

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You want to add a child which will be a

folium.GeoJson object. So this is the

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method with brackets here that creates

a GeoJSON object and for GeoJSON data we

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will use this world.JSON file. You

can find this attached in this lecture

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and let me explain what this is, but

careful, don't open it on Atom

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because if your computer is a bit slow

your atom may crash, so try to open

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it with a lighter editor such as notepad

for instance, or cat on a Linux terminal

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or Mac. Anyway this is the JSON file you

can refer to it as JSON or GeoJson.

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Actually GeoJSON is a special case of

JSON. Basically the format is always the

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same, it starts with curly brackets and

basically it contains a string which is

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like a Python dictionary with keys and

values. Keys, key and value where this

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curly bracket ends somewhere here I

believe. If I'm not wrong. This one ends

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in here, yeah. Then you have the other key,

geometry. So what is geometry? When the

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type of geometry is multi polygon so

basically you have this kind of

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attributes that describe the data.

Type multi polygon or coordinates.

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So this is now starting to describe the features,

the polygons so these are the

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coordinates over the first polygon that

will be displayed on the map. Let's say

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this is one specific country and that's

that's, that's Antigua and Barbuda, yeah.

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A small country but anyway and these are

the coordinates that will determine the

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location of the polygon in your map so

basically Folium will read all this

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information and it will decide where to put

the polygons and then you can also use

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other attributes of this such as

population which is here, yeah. You will use

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this population value to put a color for

that population and so on and so forth.

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You have all countries of the world in

this JSON file, so spend a few minutes

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looking at this file to understand its

structure and in the next lecture I'll

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go ahead and load the JSON file into

Python and display the polygon layer.

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See you there!