What is Markdown?

Markdown is a human readable syntax (also referred to as a markup language) for formatting text documents. Markdown can be used to produce nicely formatted documents including PDFs and web pages.

When you format text using Markdown in a document, it is similar to using the format tools (e.g. bold, heading 1, heading 2) in a word processing tool like Microsoft Word or Google Docs. However, instead of using buttons to apply formatting, you use syntax such as **this syntax bolds text in markdown** or # Here is a heading.

Markdown syntax allows you to format text in many ways, such as making headings, bolding and italicizing words, creating bulleted lists, adding links, formatting mathematical symbols and making tables. These options allow you to format text in visually appealing and organized ways to present your ideas.

You can use Markdown to format text in many different tools including GitHub.com, R using RMarkdown, and Jupyter Notebook, which you will learn more about this page.

Data Tip: Learn more about how you can use Markdown to format text and document workflows in a variety of tools.

Markdown in Jupyter Notebook

A great benefit of Jupyter Notebook is that it allows you to combine both code (e.g. Python) and Markdown in one document, so that you can easily document your workflows.

A Jupyter Notebook file uses cells to organize content, and it can contain both cells that render text written using the Markdown syntax as well as cells that contain and run Python code.

Thus, you can use a combination of Markdown and Python code cells to organize and document your Jupyter Notebook for others to easily read and follow your workflow.

Data Tip: Learn more about Markdown for Jupyter Notebook.

If you render your Jupyter Notebook file to HTML or PDF, this Markdown will appear as formatted text in the output document.

Data Tip: In fact, this web page that you are reading right now is generated from a Markdown document! On this page, you will learn the basic syntax of Markdown.

Benefits of Markdown for Earth Data Science

Being able to include both Markdown and code (e.g. Python) cells in a Jupyter Notebook file supports reproducible science by allowing you to:

• Document your workflow: You can add text to the document that describes the steps of your processing workflow (e.g. how data is being processed and what results are produced).
• Describe your data: You can describe the data that you are using (e.g. source, pre-processing, metadata).
• Interpret code outputs: You can add some text that interprets or discusses the outputs.

all in one document!

When used effectively, Markdown documentation can help anyone who opens your Jupyter Notebook to follow, understand and even reproduce your workflow.

Format Text in Jupyter Notebook with Markdown

Markdown Cells in Jupyter Notebook

In the previous chapter on Jupyter Notebook, you learned how to add new Markdown cells to your Jupyter Notebook files using Menu tools and Keyboard Shortcuts to create new cells.

You also learned how to change the default type of the cell by clicking in the cell and selecting a new cell type (e.g. Markdown) in the cell type menu in the toolbar. Furthermore, you learned that in a Jupyter Notebook file, you can double-click in any Markdown cell to see the syntax, and then run the cell again to see the Markdown formatting.

Note: if you type text in a Markdown cell with no additional syntax, the text will appear as regular paragraph text. You can add additional syntax to that text to format it in different ways.

On this page, you will learn basic Markdown syntax that you can use to format text in Jupyter Notebook files.

Section Headers

You can create a heading using the pound (#) sign. For the headers to render properly, there must be a space between the # and the header text.

Heading one is denoted using one # sign, heading two is denoted using two ## signs, etc, as follows:

## Heading Two

### Heading Three

#### Heading Four

Here is a sample of the rendered Markdown:

Heading Three

Heading Four

Note: the titles on this page are actually formatted using Markdown (e.g. the words Section Headers above are formatted as a heading two).

Lists

You can also use Markdown to create lists using the following syntax:

* This is a bullet list
* This is a bullet list
* This is a bullet list


1. And you can also create ordered lists
2. by using numbers
3. and listing new items in the lists 
4. on their own lines

It will render as follows:

• This is a bullet list
• This is a bullet list
• This is a bullet list

1. And you can also create ordered lists
2. by using numbers
3. and listing new items in the lists
4. on their own lines

Notice that you have space between the * or 1. and the text. The space triggers the action to create the list using Markdown.

Bold and Italicize

You can also use ** to bold or * to italicize words. To bold and italicize words, the symbols have to be touching the word and have to be repeated before and after the word using the following syntax:

*These are italicized words, not a bullet list*
**These are bold words, not a bullet list**

* **This is a bullet item with bold words**
* *This is a bullet item with italicized words*

It will render as follows:

These are italicized words, not a bullet list These are bold words, not a bullet list

• This is a bullet item with bold words
• This is a bullet item with italicized words

Highlight Code

If you want to highlight a function or some code within a plain text paragraph, you can use one backtick on each side of the text like this:

`Here is some code!`

which renders like this:

Here is some code!

The symbol used is the backtick, or grave; not an apostrophe (on most US keyboards, it is on the same key as the tilde (~)).

Horizontal Lines (Rules)

You can also create a horizontal line or rule to highlight a block of Markdown syntax (similar to the highlighting a block of code using the backticks):

***

Here is some important text!

***

which renders like this:

Here is some important text!

Hyperlinks

You can also use HTML in Markdown cells to create hyperlinks to websites using the following syntax:

<a href="url" target="_blank">hyperlinked words</a>

You can identify the words that will be hyperlinked (i.e. prompt a web page to open when clicked) by replacing hyperlinked words in the example above.

For example, the following syntax:

Our program website can be found at <a href="http://earthdatascience.org" target="_blank">this link</a>.

will render as follows with this link as the hyperlinked words:

Our program website can be found at this link.

Render Images

You can also use Markdown to link to images on the web using the following syntax:

![alt text here](url-to-image-here)

The alt text is the alternative text that appears if an image fails to load on webpage; it is also used by screen-reading tools to identify the image to users of the screen-reading tools.

For example, the following syntax:

![Markdown Logo is here.](https://www.fullstackpython.com/img/logos/markdown.png)

will render as follows with an alt text of Markdown Logo is here.:

Local Images Using Relative Computer Paths

You can also add images to a Markdown cell using relative paths to files in your directory structure using:

![alt text here](path-to-image-here)

For relative paths (images stored on your computer) to work in Jupyter Notebook, you need to place the image in a location on your computer that is RELATIVE to your .ipynb file. This is where good file management becomes extremely important.

For a simple example of using relative paths, imagine that you have a subdirectory named images in your earth-analytics directory (i.e. earth-analytics/images/).

If your Jupyter Notebook file (.ipynb) is located in root of this directory (i.e. earth-analytics/notebook.ipynb), and all images that you want to include in your report are located in the images subdirectory (i.e. earth-analytics/images/), then the path that you would use for each image is:

images/image-name.png

If all of your images are in the images subdirectory, then you will be able to easily find them. This also follows good file management practices because all of the images that you use in your report are contained within your project directory.

Data tip: There are many free Markdown editors out there! The atom.io editor is a powerful text editor package by GitHub, that also has a Markdown renderer that allows you to preview the rendered Markdown as you write.