Adding Additional Marks

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En provenance du cours de New York University Tandon School of Engineering

Information Visualization: Programming with D3.js

28 notes

New York University Tandon School of Engineering

Information Visualization: Programming with D3.js

28 notes

Cours 3 sur 4 dans Specialization Information Visualization

In this course you will learn how to use D3.js to create powerful visualizations for web. Learning D3.js will enable you to create many different types of visualization and to visualize many different data types. It will give you the freedom to create something as simple as a bar chart as well your own new revolutionary technique. In this course we will cover the basics of creating visualizations with D3 as well as how to deal with tabular data, geography and networks. By the end of this course you will be able to: - Create bar and line charts - Create choropleth and symbol maps - Create node-link diagrams and tree maps - Implement zooming and brushing - Link two or more views through interaction The course mixes theoretical and practical lectures. We will show you step by step how to use the library to build actual visualizations and what theoretical concepts lie behind them. Throughout the course you will learn skills that will lead you to building a whole application by the end of the lectures (a fully working visualization system to visualize airlines routes). This course is the third one of the “Specialization in Information Visualization". The course expects you to have some basic knowledge of programming as well as some basic visualization skills.

À partir de la leçon

Lines, Arcs, and maps

Projections3:36

Drawing Maps5:17

Practice: Drawing Base for Map10:01

Choropleth Map3:05

Practice: Choropleth Map12:51

Adding Additional Marks3:41

Practice: Adding Additional Marks7:35

Rencontrer les enseignants

Enrico Bertini
Associate Professor
Computer Science and Engineering
Cristian Felix
PhD. Candidate
Computer Science and Engineering

Why one option is to map the information that you want to communicate?

Should the country borders or state border or whatever thing you're visualizing,

that's not always possible or not always recommended.

So, in some cases,

color is a problem for people to understand what's happening.

They are also affected by the area of the country.

So if you want to avoid these problems,

you may want to add the new marks instead of just using the ones that you have.

Another situation where you want to add new marks is when

what you are mapping doesn't map to a specific country,

for example, but mapping to a specific longitude and latitude.

So, for example, if I'm visualizing cities,

I going to draw first the countries to know where the cities are,

and then you're going to draw a dot on each country to

represent where in the country the city is.

So, those are the cases where we need additional mark

and we won't be using the ones that we draw as base for a map.

So, for example, here we created a base-map where we are

visualizing the countries and the region just as reference to the user.

Those map doesn't contain any data that we are looking to communicate.

But then, on top of that,

we draw dots representing each earthquake that we had in the past 100 years.

So this means that I can look where the earthquake happens,

but now I can also correlate to the countries and see if there is

a specific regions of the globe where we have more earthquakes than other regions.

The way it happens is,

if I have something that has a latitude and a longitude,

I can translate that to x and y in the pixel's coordinate using the projection.

So we have been using projections,just passing it to the geo-path,

but now we can also use projections the same way we use the scales.

We used the scales in the past to map, for example,

a date time to a x and y position,

and we values categorical values as well to x and y are callers.

Projection works as a scale,

so you can give latitude and longitude to projections and get back x and y positions.

For example, I can create a geoMercator projection,

and then using this projection I can create my marks.

So the way create marks is the exact same way

I would create anything in any correlative authorization.

So think about the scatterplot.

It would be adding those circles,

and you would set the x and y position of the circle.

So, the difference here is that the way I set the x and y position.

So instead of using the scale,

I going to use my projection theta I called p and I going to pass

the longitude and latitude of my data as parameter to just projection,

and I going to get also an array that contains the x and y position.

So that's why here, for example,

I am changing to zero and to one because I'm getting both.

I get an array as outputs so the zero is going to represent the x,

and the one is going to represent the y position of the circle.

Once I did that,

the circle is going to be in their

geographical position that I expect it to expected to be,

representing that specific event, for example,

happened on that specific region and you get your final map.

Those type of association is really powerful because by combining multiple dots,

you end up with some patterns and trends that would be harder to see another way.

So, for example here,

you can almost see the borders of the tectonic plates that cause some of

the earthquakes that we had by merging those points

together and seeing how they position themselves around the globe.

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