# How to create a quiver plot with vectors and a color map?

by Dejaswarooba Updated: Jul 10, 2023

Solution Kit

Quiver plots are also known as quiver charts. They are a powerful tool in data visualization. It allows us to represent vector fields using arrows. They can be enhanced by incorporating a color map. It results in a colored quiver plot that adds another dimension of information. Creating a simple quiver plot involves specifying the quiver arrow color argument. We can do it using the function quiver of the Matplotlib library.

This function allows us to control the arrows' direction, size, and color. When plotting a stream plot of parallel lines, we can use Matplotlib's subplot method. It displays many plots, with the first subplot representing the quiver plot arrows. Then, the second subplot displays the colored quiver plot.

In a quiver plot, the arrow units and length units can determine the scale of the arrows. The data point coordinates determine the arrow starting point and locations. The first arrow originates from the original arrow. The vector field or directional components determine the arrow directions. Many arrows can represent different vectors. At the same time, a single arrow can display the magnitude and vector direction. By adding a second arrow or a third arrow, we can represent extra vectors or forces in the same plot.

The arrow vectors provide visual insights into the velocity or electric field gradients. They can be oriented in any other direction, depending on the data. The current axes, the horizontal axis, can accommodate the plot. The scale parameter determines the arrow size. A smaller scale parameter results in smaller arrows. You can analyze the directional components or stream velocity. You can observe the relative lengths and orientations of the arrows.

To create a colored quiver plot, we can specify a color sequence or colormap. It assigns colors to the arrows based on magnitude or another variable of interest. This helps us visualize the variation of the attribute across the vector field.

Quiver plots find applications in fluid flow analysis. It is where they can represent velocity vectors or gradient fields. They are used to visualize vector lines, stress gradients, and vortices. The position arrays in the x-y plane can create the quiver plot. It can adjust the plot width and axis limits, allowing for better data visualization. Tick labels and tick marks provide reference points and line styles. They enhance the field lines and colormaps to understand the data distribution.

### Syntax of quiver function

The syntax of the `quiver` function in matplotlib is as follows:

*quiver(X, Y, U, V, [C], **kwargs) *

where:

- `X` and `Y` are the coordinates of the arrow locations. They can be 1D or 2D arrays specifying the x and y coordinates.
- `U` and `V` are the components of the arrow vectors, specifying the arrow directions in the x and y directions. They can also be 1D or 2D arrays of the same shape, like `X` and `Y`.
- `[C]` (optional) is an array or sequence of values representing the color of each arrow. It can assign colors to the arrows based on some attribute or magnitude.
- `**kwargs` are extra keyword arguments that allow you to customize the arrow appearance. Some common kwargs include `color`, `scale`, `width`, `headwidth`, `headlength`, `headaxislength`, `units`, and `angles`. These arguments control the color, scale, width, size, and other arrow properties.

Note that the `quiver` function can plot 2D and 3D vector fields. It depends on the input arrays' dimensions.

### General steps to create a quiver plot using Matplotlib:

- You can use the quiver plot arrows or quiver charts to create a quiver plot with vectors and a color map. You can use the `quiver` function.
- You must define the positions and directions of the arrows using position arrays in the x-y plane. It can be created using the `meshgrid` function or a uniform integer meshgrid.
- Next, you can create subplots using the `subplots` method to have many plots in one figure. In each subplot, you can use the `quiver` function. It plots the arrows with specified arrow locations, directions, and lengths.
- Using appropriate arguments, you can adjust arrow size, length unit, and starting point. You can specify the arrow color using the `color` argument, a single color, or a color sequence.
- To add a color map, you can use colormaps in matplotlib. It provides various colors to represent the magnitude associated with the vectors.
- Finally, you can customize the plot by adding tick labels. You can also adjust the line style, set the axis limits, and add grid points if needed.
- These plots help visualize fluid flow velocities, electric fields, stress gradients, or vortices. It can be a useful tool in various scientific and engineering applications.

*Preview of the quiver() function in matplotlib with color map.*

**Code**

The code here creates a quiver plot that shows a field of 10 vectors, each with a randomly generated position, angle, velocity, and likelihood of occurrence. The occurrence probability, which is normalised and mapped to the "copper" colour map using a scalar mappable, determines the colour of each vector. Using Matplotlib's **plt.quiver() **function, which takes the x and y coordinates of the vectors, along with their x and y components and color., the quiver plot is created.

__Follow the steps carefully to get the output easily.__

- Install Visual Studio Code in your computer.
- Install the required library by using the following command - pip install matplotlib
- If your system is not reflecting the installation, try running the above command by opening windows powershell as administrator.
- Open the folder in the code editor, copy and paste the above kandi code snippet in the python file.
- Remove the first line from the code.
- Run the code using the run command.

I hope you found this useful. I have added the link to dependent libraries, version information in the following sections.

*I found this code snippet by searching for "**How to create quiver plot with vectors and color map**" in kandi. You can try any such use case!*

**Dependent libraries**

matplotlibby matplotlib

matplotlib: plotting with Python

matplotlibby matplotlib

Python 17559 Version:v3.7.1 License: No License

If you do not have matplotlib that is required to run this code, you can install it by clicking on the above link and copying the pip Install command from the page in kandi.

*You can search for any dependent library on kandi like **matplotlib*.

### Environment tested

- This code had been tested using python version 3.8.0
- matplotlib version 3.7.1 has been used.

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### FAQ

**1. What is a quiver plot, and what are the arrows used for? **

A quiver plot is a visualization that represents vector fields using arrows. The quiver plot arrows indicate the vector's magnitude and direction at specific points. It provides a visual representation of velocities, forces, or electric fields.

**2. How do I use the quiver arrow color argument to change the colors of my arrows? **

You can use the `color` argument in the `quiver` function to change the colors of your arrows. It provides a single-color or an array/sequence of values representing each row color.

**3. What is the arrow length unit of measurement when plotting with Python?**

The length depends on the scale parameter when plotting with the quiver function. The length of the arrows is determined relative to the scale parameter. It can be adjusted to control the size of the arrows in the plot.

**4. How do I determine where the arrow starting point should be on a graph? **

The arrow starting point on a graph is determined by the x and y coordinates. It is specified in the `X` and `Y` arrays passed to the `quiver` function in matplotlib. The starting point of each arrow corresponds to the corresponding x and y coordinate pair in the `X` and `Y` arrays.

**5. Are there specific rules for plotting arrow directions in a quiver plot? **

In a quiver plot, the arrow directions are determined by the components specified in the `U` and `V` arrays. The arrow length represents the magnitude. Then, the arrow direction represents the direction of the vector field at that point.

**6. Does Python support 3D Arrow Vectors in its Quiver Plot function?**

Yes, Python supports 3D arrow vectors in its Quiver Plot function in Matplotlib. The `quiver` function can plot 3D vector fields. It provides three-dimensional arrays for the arrow positions and directions.