Discover Interpolation

How do we get a continuous map from discrete data points?

Much of the data that we have looked at in the Seagrass Adventure were created using interpolation. Interpolation is a method in which the value of data points in unsampled areas is estimated using measurements from nearby sites. Scientists use this technique because there is never enough time or money to measure every point in the area of interest.

Interpolation is based on Tobler’s Law of Geography, which states that “everything is related to everything else, but near things are more related than distant things” 1. In other words, points closer together in space are more likely to have similar values than points that are farther apart. This is called ‘spatial autocorrelation’. Interpolation is used in many fields, from photography to geology to GIS and remote sensing.

Putting it into practice

Now that we know interpolation is, let’s put it into practice. To estimate water quality, multiple stations were set up in the Bay and measurements, such as chlorophyll a and total nitrogen were taken. Then, the data from each station were inputted into a computer algorithm to estimate the values of the areas in between the points. This way, we could use only a few stations to learn about the entire bay.

There are many different computer algorithms used to interpolate data points. Depending on which one you use, the final map can look different. Scientists choose between different algorithms based on the type of data and how the data will be used.

Try it at home

Here’s an activity that you can do at home:
Put 3-5 M&Ms in a petri dish or low clear dish with water in it. Watch the colors merge. When you are done, empty the dish and try it again using several different arrangements of color and position.