# How to Use alpha with geom_point() in ggplot2

You can use the alpha argument within the geom_point() function in ggplot2 to modify the transparency of the points in a plot.

This argument uses the following basic syntax:

```ggplot(df, aes(x=x, y=y)) +
geom_point(alpha=1)
```

The value for alpha can range between 0 and 1 where:

• 0 is completely transparent
• 1 is completely solid

The default value for alpha is 1.

By setting alpha to a value less than 1 it becomes easier to view overlapping points in a plot, which is particularly useful when plotting the points of a large dataset.

The following examples shows how to use the alpha argument in practice with the following data frame that contains 5,000 rows:

```#make thise example reproducible
set.seed(1)

#create data frame with 5000 rows
df <- data.frame(x=runif(n=5000, min=1, max=100))

df\$y = df\$x*3 + runif(5000)*df\$x^2

x         y
1 27.28536  108.2851
2 37.84027  622.8478
3 57.71248 1002.0662
4 90.91257 7539.2476
5 20.96651  202.6813
6 89.94058 2867.4643
```

Related: How to Use runif Function in R

## Example 1: Using alpha = 1 in geom_point()

The following code shows how to create a scatter plot in ggplot2 by using the default value of 1 for the alpha argument:

```library(ggplot2)

#create scatter plot with default alpha value
ggplot(df, aes(x=x, y=y)) +
geom_point()
```

Notice that the points in the plot are completely solid, which corresponds to an alpha value of 1.

## Example 2: Using alpha = 0 in geom_point()

The following code shows how to create a scatter plot in ggplot2 by using a value of 0 for the alpha argument:

```library(ggplot2)

#create scatter plot with alpha value of 0
ggplot(df, aes(x=x, y=y)) +
geom_point(alpha=0)
```

All of the points in the plot are completely transparent, which corresponds to an alpha value of 0.

## Example 3: Using alpha = 0.1 in geom_point()

The following code shows how to create a scatter plot in ggplot2 by using a value of 0.1 for the alpha argument:

```library(ggplot2)

#create scatter plot with alpha value of 0.1
ggplot(df, aes(x=x, y=y)) +
geom_point(alpha=0.1)
```

By setting alpha to 0.1, the points have a level of transparency that allows us to see where the points overlap the most on the plot.

Feel free to play around with the value of alpha within the geom_point() function to achieve a level of transparency that makes your plot the easiest to read.