Plastic Pollution

Plastic pollution is a rather new but exponentially growing phenomenon. Annual global plastic production has exploded over the past decades, going from some 1.5 million metric tons (MT) in 1950 to an astonishing 368 million MT in 2019. Furthermore, plastic production is expected to further increase in the coming decades as current investments in petrochemical infrastructure support this trend. Under business-as-usual scenarios, annual production could reach up to 2’000m MT by 2050.

You've been asked to create a map that portrays crucial information about plastic pollution such that the group of stakeholders can start defining some strategies to tackle the problem. You will use Map Viewer Classic, which allows you to create and interact with spatial data through online maps. First, we'll explore existing spatial data to visualize the distribution of microplastic in the ocean. Next, we will construct a web map by searching and adding layers to an empty web map. Once you add the necessary layers, you will modify symbology and customize other map properties, such as the organization of attributes that display when you click a feature on the map. Last, you'll share your map as a professional-looking web app using StoryMaps so other users can explore it.

Some of the questions to address with the map are:

• What are the countries that contribute the most to plastic pollution in the ocean?
• Where are the potential main point sources of plastic pollution to the ocean? (data on river pollution)
• How is plastic pollution distributed in our oceans?

In order to answer these questions, we will use spatial data to perform a simple spatial analysis and identify potential main point sources of plastic pollution. We will also create maps that portrait the spatial distribution of plastics in our oceans.

• Utilize ArcGIS Online to import and visualize spatial data
• Explore data visualization styles and techniques (classification quantity)
• Configure pop-ups
• Apply basic spatial analysis –hotspots analysis or data aggregation and summarize
• Evaluate the use of maps for decision-making
• Share the information using a webmap

Before we start, it is important to talk about Spatial Data, the different models of representation and the different formats. The most important distinction about spatial data is that there are two types of representation models in GIS,  Raster and Vector . The main difference between Raster and Vector Data is that the raster data represents data as a cell or a grid matrix while vector data represents data using sequential points or vertices.

Raster

 Raster  data is any pixelated (or gridded) data where each pixel is associated with a specific geographical location. The value of a pixel can be continuous (e.g. elevation) or categorical (e.g. land use). If this sounds familiar, it is because this data structure is very common: it's how we represent any digital image (i.e., a photo).

Vector

In the  vector-based model , geospatial data is represented in the form of coordinates and the basic units of spatial information are points, lines (arcs), and polygons. Each of these units is composed simply as a series of one or more coordinate points, for example, a line is a collection of related points, and a polygon is a collection of related lines. In this tutorial, we will work with vector data only.

Attributes

Spatial data contains more information than just a location on the surface of the Earth. Any additional information, or non-spatial data, that describes a feature is referred to as an  attribute  or tabular data. Spatial data can have any amount of additional attributes accompanying information about the location. For example, in this tutorial, you will work with the location of plastic pollution; in addition to their location, you will find additional attributes such as the type of plastic, weight, etc.

Data Formats

There are a lot of data formats and/or file extensions for encoding  geographical information  into a  computer file . They are created mainly by government mapping agencies (such as the  USGS  or  National Geospatial-Intelligence Agency ) or by  GIS  software developers. Please give a look at  Some common open formats for spatial data , which describes in detail some of the spatial data formats that can stand alone on your hardware.

You will use Map Viewer Classic to build an online map. First, you will explore existing spatial data provided as a comma-separated value (CSV) file that contains  georeferenced locations with latitude and longitude . This file is being shared with you through the ArcGIS Online platform (see process below) or you can download the data through  figshare  (1).

• Click on  ArcGIS Online Login 
• Login by clicking on “ YourArcGIS organization’s URL” 
• Type in Tuftsgis - If this is your personal computer, click Remember this URL and click Continue.
• Use your Tufts Username and password to sign in and complete the duo request.
• Click on Groups  ArcGISOnline Lesson - Environmental Problem Solving DHP P250 
• Go to Content
• Navigate to Files (Item type)
• Download the  Plastic_Marine­_Pollution_Global­_Dataset_Eriksen­_etal_2014  CSV file (Erikson et al., 2016) to your computer and open it.
• Save it in a folder you will remember (e.g., Downloads)

Every new map starts with a basemap. This tutorial assumes that your default basemap will be a the Topographic basemap and that its default extent is the world. If your settings are different, you'll make changes as needed in the first section. To create a map, complete the following steps:

• Click Map at the top menu.

• The  New Map Viewer  will open.

For the purpose of this tutorial, we will change to the Map Viewer Classic.

• Click at the upper right part of the map, Open in Map Viewer Classic.

• A new map will appear with a different view.

Your map's appearance might vary based on your account or organizational settings and your browser window size. It may show the United States, the world (such as in the example image), or another extent. The only layer on the map is the basemap, which provides geographic context such as water bodies and political boundaries.

Next, you'll add a layer to your map that shows the distribution of microplastics in the ocean.

• In the Layers pane, click the first tool Add > Add Layer from File

Read about the different formats you can add.

• Click on Choose File and locate the file you just downloaded in the correct folder.
• Select the file and click Open > Import Layer

Map Viewer reads the geographic information in your file and displays (aka Stylizes) one of the fields in the data attribute table so you can immediately see patterns.

• In the Change Style pane, note that the attribute being shown is the Total Particles per Km2; it means, it is using a field named as such to classify the data.
• Under drawing style > Counts and Amounts (Size), click Options.
• Click Symbols.
• Under Fill, select No Color.
• For Outline chose a dark orange color (such as #FF5500).
• Change the Transparency to 25%. Note: simply use the bar to control transparency
• Click OK twice.
• Click Done to finish changing the style of your layer.

The end result of the symbology selected shows different-sized circles that represent a total count of plastic (pieces km−2). The larger the circle, the more plastic pieces counted for that particular location.

 Basemaps  provide realistic depictions of the earth at multiple scales and use authoritative data as reference sources. The default Topographic basemap that you probably got in your webmap, is better suited for a reference map than a  thematic map . You'll change the basemap to something that might serve better our purpose.

• Click Basemap and explore the different options of base maps.
• Choose different basemaps such that you can see how they served the purpose of providing context and a background to our main data (microplastics).
• For the purpose of this tutorial, choose Oceans.

The circles show information that is helpful to us in identifying areas of plastic pollution in the ocean. Currently, we are looking at Total Particles per Km2. Look at the different attributes available by clicking on the “show table” icon and explore the different data available. Keep them in mind.

Now, it is time to save your project.

• Click Save (upper tool menu); choose Save.
• In the Save Map window, provide a title, tags, and a summary.
• Title: World Plastic Pollution (your Name and Last Name).
• Tags: Marine Plastic Pollution, GIS, DHP250,
• Summary: DHP250 ArcGIS Online Tutorial on Plastic Pollution.
• Save in folder:
• Click Save Map. This saves the map in your personal AGOL folder. Right now, no one else has access to this map. Make sure to save regularly!

By saving your map, you also created a corresponding item page that contains a variety of information, actions, options, and settings. This is called  Metadata .

Additional layers with information about plastic pollution will be added to provide more context and information. These will help us support decisions in relation to the questions posted at the beginning of this tutorial.

• On the ribbon, click Add and choose Search for Layers.
• Click the dropdown arrow next to My Content and choose My Groups.
• Find the following two layers: 1) Plastic Pollution by Country, and 2) Global Riverine Plastic Emissions.
• In the list of results, click the little Add button on both layers.

These two layers have been previously added for you into the class group in the cloud. These data come from two sources: a) Hannah Ritchie and Max Roser, 2018 (2) and b) Meijer et al., 2021 (3), which is also available through an interactive platform called  River Plastic Emissions to The World's Oceans .

Note: It might take some time to display due to the amount of information.

We can always make the process more efficient by turning off and on some of the layers and also, by changing their names when necessary. For example, to explore the spatial distribution of the data, we can turn on and off some layers such that we can leave one layer visible at a time. Let's try.

• Turn off all layers but the Plastic Pollution by Country.

Tip: you can turn off them all at the same time by pressing the Ctrl key and turning one-off.

• Reorder the layers such that Plastic Pollution by Country is at the bottom of the list.
• You just need to click on top of the layer and without letting the click go, drag the layers (e.g., Plastic Pollution by Country) to the top or bottom.
• Open the Attribute Table to explore the table and search for a field to stylize our data.

Think about some of our questions posted at the beginning of the exercise and how this map will support some decisions. One of those questions is: What are the countries that contribute the most to plastic pollution in the ocean?

If we are preparing a map on plastic pollution by country, what information (field) might be useful to classify countries with?

We have a couple of options if we look at our attribute table:

• Share of plastic inadequately managed
• Mismanaged waste (% global total)
• Plastic waste generation (tonnes, total)
• Per capita plastic waste (kg/person/day)
• Mismanaged waste in 2025 (% global total)
• Share of global mismanaged plastic waste (2019)

We can select any of these fields to change the style for the Plastic Pollution by Country layer to display the data. Let's start with the field Per capita plastic waste (kg/person/day).

• Close the Attribute table
• On the Plastic Pollution by Country, click on the Change Style icon.
• Choose an attribute to show. Select Per capita plastic waste (kg/person/day) field.

We will have different style options to visualize our data by  quantities .

• Select Counts and Amounts (Color).
• Click on Options.
• Click on Symbols and select a color ramp that might better have an impact to show this data for example, an orange gradient color scheme might work.

The default symbolization is called “Stretched” in which a continuous color or grayscale is used to show map values ranging from lowest to highest. In other words, the colors are stretched from low to high. ArcGIS Online allows you to explore your data in different ways through a variety of smart mapping styles. When you use  Change Style , the nature of your data determines the styling suggestions you see by default. However, you can determine what classification methods you can use.

Changes to the data’s appearance can always be made that is, you have control over styling elements such as color ramps, line weights, transparency, and symbols. Let’s try to change the color ramp to something more exciting.

• Click on Classify Data

Look at the bar and the four classes determined by the classification method (Natural Breaks).This  classification method  are based on natural groupings inherent in the data. Class breaks that best group similar values and that maximize the differences between classes.

Play around with the different classification methods under Classify Data. Once you play around selecting different classification methods, let’s go select Natural Breaks and change the classes to 5.

• Click OK twice. Then click Done.

The  Living Atlas  is an excellent source of highly curated datasets, maps, and apps collected by ESRI and compiled within the ArcGIS Online infrastructure. It allows you to easily search and add ready-to-use data to your map. Make sure you explore it  here !

• Click again on Add > Browse Living Atlas Layers
• Type in “ocean currents” and then select Major Ocean Currents by Maps.com_Carto.
• Click on the name of the layer to read more about the data, what it represents and how it was collected.
• Click the plus sign or “Add to Map” in order to add the layer to your map
• Now you can see some possible patterns for the accumulation of plastic in the ocean by currents.

For more information on the potential role that currents play in plastic pollution transport and behavior in the ocean, look at the following article by Gennip et al., (2019):  In search for the sources of plastic marine litter that contaminates the Easter Island Ecoregion .

Understanding the characteristics of the spatial data distributions helps understand appropriate analysis methods to reach reasonable conclusions from your analysis. Spatial patterns deal with both the distributions of values (attributes) and the spatial arrangement of the locations. Summarizing spatial characteristics can, more clearly, show patterns in data.

Let's work with the Global Riverine Plastic Emissions. If you look at that layer (turn it on), you will notice that it has a large number of points. When you enable clustering, Map Viewer groups point features that are within a certain distance of one another on the map into one symbol. Clustering allows you to see patterns in the data that are difficult to visualize when a layer contains hundreds or thousands of points that overlap and cover each other. 

Explore the attribute table of Global Riverine Plastic Emissions and look at the available data.

• Open the attribute table.
• Explore the different fields.

Note: you can turn on and off the different columns - this makes more manageable the table when exploring or looking at the values of different fields.

• On the attribute table, go to Options (at the top-right > three lines).
• Click on Show/Hide Columns
• Turn on and off some columns so you can see the result.
• Once you are done exploring, close the table.

Note: you are not deleting the columns, you are just hiding them.

The data is represented with a single symbol and many of these point locations, seem to overlap from a global perspective. We will cluster those points using a tool called Cluster Points.

• Click below the layer's name and select the tool Cluster Points.
• A window will open. You can move the bar to change the cluster to fewer or more points.
• Once you are satisfied with the result, click OK.

Point datasets with a large number of dense features inevitably overlap, hiding any potential meaning within the data. A heat map uses the features in the layer to calculate and display the relative density of points on the map as smoothly varying sets of colors ranging from cool (low density of points) to hot (many points) – hence the name heat map.

With the same point data - Global Riverine Plastic Emissions - we will create a heat map. But first, let's make a copy of our layer.

• Click on More options > Copy.
• Turn off the layer we used to apply the clustering.

A new copy of the layer Global Riverine Plastic Emissions will be created.

• Under the new layer, go to Cluster Tool to remove the clustering.
• Uncheck the option Enable Clustering.
• Click OK.
• Click on Change Style.
• Under Heat Maps, choose an attribute to show, select Plastic Emissions (tons).
• Click on OPTIONS > SELECT.
• Explore the different options of Area of Influence, Transparency, and Visible Range.
• Once you are done exploring and deciding the different settings, click OK.

You can see now how patterns are revealed!

Remember, If your data contains numeric attributes (in our case, plastic emissions in tonnes), the heat map can weight this data to calculate the optimal display. In this heat map of plastic emission by river outlet, the number of plastic emissions in tons is applied as a weight.

As a final step and to distinguish between the two Global Riverine Plastic Emission layers, you can change the name of the layer.

• Select the Global Riverine Plastic Emission - copy and go to Options
• Click on Rename.
• Assign a name of your preference to note in each layer that one uses clusters, and the other one a heat map method of representation.
• Click OK once you are done.

Please take a minute to explore those areas where higher emissions of plastic through river outlets are located and turn on the other layers to compare them all.

It is important to distinguish between the foreground and background on a map. This can be done by adding some contrast. Let's change the basemap again to reveal even more patterns and provide contrast with your symbology selection. Select the Light Gray Canvas or the Dark Gray Canvas basemap and try them both!

If you would like to know more about the method of classification, please visit  HeatMap  documentation.

Pop-ups contain information about features and images in map layers. Pop-ups can include attachments, images, charts, and text, and they can link to external web pages. It is important to note that the default pop-up appearance for a feature layer—if the layer owner has not configured it—is a table of attributes and values. So if you look at the attribute table of each of your layers, and then you click on top of any feature display on the map, it will show jus that. Let's try!

The layer owner can save a new configuration, which is why the pop-ups in a map can display relevant information without additional steps by the map author. Hence, if you think about the decision-makers or audience who will access this information, you can also decide what's the crucial information that will facilitate a decision-making process.

Let's start working with the PollutionGlobalDataset_eriksen_etal_2014 (marine plastic pollution by Eriksen et al., 2014) layer.

• We will rename the layer first to Marine Plastic Pollution.
• Click the More Options button, and choose Configure Pop-up.
• In the Pop-up Title field, write Plastic Sample Site.

• For Pop-up Contents, change Display to A custom attribute display and click Configure
• In the Custom Attribute Display window, click the Add field name button and choose {Total_Particles_per_Km2} and {Total_weight_g_km2_}. Add a space in between such that you can add them both. In this step, we are choosing which of the attribute fields we want to automatically pop up when we click on a point in the map.
• Next, we are going to format this information nicely so it reads like a sentence. Type A total of before the field {Total_Particles_per_Km2} and pieces with a total weight of before {Total_weight_g_km2_}, followed by g/Km2.
• Click OK and click OK again to save your changes and close the configure pop-ups window.
• Click a circle in the map to see your revised pop-up.

Note: Make sure to adjust the formatting and emphasis appropriately. Notice the other formatting options available when configuring pop-ups. And, don't worry, you haven't lost your data. You can still see it by showing the attribute table.

Let's continue now with the Plastic Pollution by Country layer.

• Click in More Options and choose Configure Pop-up.

In the Pop-up Title field, we have the field {NAME}. This means that Every time you click on top of one of these objects on the map, its name will appear at the top of the pop-up.

Below, you will see the Pop-up Contents.

• We will click on Configure Attributes.

The window of Configure Attributes will allow you to select those attributes you want to show. You can turn on and off all of them by clicking on the box of Display.

Not all of the attribute table fields are relevant for our purpose hence, we will only select those that provide some information about plastic management.

Select the following fields only:

• Share of plastic inadequately managed
• Mismanaged waste (% global total)
• Plastic waste generation (tonnes, total)
• Per capita plastic waste (kg/person/day)
• Mismanaged waste in 2025 (% global total)
• Share of global mismanaged plastic waste (2019)

For each one of them, select either use 1000 Separator; and 2 decimal places on the Format.

• Click OK.

For the rest of the layers, we will turn-off the pop-ups.

• Point to the Global Riverine Plastic Emissions layer (both layers), click the More Options button, and choose Remove Pop-up.

This will block the pop-ups for this layer. This action can be reverted later if needed.

One of the questions included to help in a decision-making process is

Where are the potential main point sources for plastic pollution to the ocean?

Imagine you've been tasked to evaluate all sites (coastal and marine) to increase monitoring efforts. This evaluation is based on finding those hotspots - the presence of large amounts of plastic entering the ocean and in the ocean. How do you evaluate these sites in a quantifiable and defensible way? Of course, you need data, but so far, we can work with the datasets we have and analyze them to measure geographic relationships and clusters.

When we look at a map, we inherently start turning that map into information by finding patterns or assessing trends. This process is called spatial analysis and it help us make decisions. However, if we look at the data, we might not be able to look at any pattern or relationship; our datasets are global and these characteristics aren't always obvious by looking at a map. The way we display the data on the map can change the patterns we see. For instance, our layer of plastic marine pollution shows those sites where more pieces of plastic by Km2 or more weight (g/Km2) was found. Spatial analysis tools allow us to quantify patterns and relationships in the data and display the results as maps, tables, and/or charts. Using spatial analysis tools, we can answer questions and make decisions using more than a visual analysis.

 Hotspot analysis  is a spatial analysis and mapping technique used in the identification of statistically significant clustering of spatial phenomena. We will use it to answer our question of where we can find the main point sources for plastic pollution to the ocean. These spatial phenomena can be depicted as points in a map and refer to locations of events or objects.

We currently have the Global Riverine Plastic Emissions layer (Meijer et al., 2021) and we can apply a hotspot analysis, which currently is being represented using the Heat Map symbology.

• Click on Analysis tab
• Expand the Analyze Patterns > Click on Find Hot Spots

Note: you can click on the i (aka identify) to learn more about the tool.

• Select any of the Global Riverine Plastic Emissions layers (they both come from the same file, it is just repeated in the Contents' Pane).
• For Find cluster of high and low, select the Plastic Emission (tons)
• Rename the Result layer name as: Hot Spot Riverine Plastic Emissions_your_initials

Important: Make sure to zoom out so all the data is in view before running the analysis. Alternatively, you can uncheck the “Use current map extent” option.

The output from the Find Hot Spots tool is a map layer. For the points or the areas in our result layer map, the darker the red or blue colors appear, the more confident you can be that clustering is not the result of random chance – but it is in fact, statistically significant.

Expand the symbology so you can see the confidence intervals in the results - turn off the other layers to appreciate the results.

The analysis shows those places from red (hot spot) to blue (cold spot). Sites with no significant data are presented in gray.

Sometimes the results of your analysis will indicate that there are no statistically significant clusters at all; this usually happens when a spatial pattern is random. However, when you do find statistically significant clustering, the locations where clustering occurs are important clues about what may be creating the clustering.

Now you can visually compare two layers, the Plastic Pollution by Country and the Hot Spots Plastic Emission analysis results and determine if the hot spots coincide with those countries that have the highest waste generation. Also, you can use other indicators to compare such as the share of plastic inadequately managed, per capita plastic waste, etc. (see the attribute table for Plastic Pollution by Country).

What decisions do you think this information supports when identifying hotspots based on our data?

To display a summary of the analysis, click on Show Result. The report outlines the workflow and the number of data points (Hot Spot Analysis) that are statistically significant.

Before sharing our map, it is important to make sure we provide enough background information about the data we are using for our map. This will provide credibility not only to the map but also, to the decision-making process.

We are almost done. Make sure to SAVE the process you have made.

• In the Contents pane, click the About button.
• Click More Details to open the item page.

Your map's item page opens in a new window. The item details are missing important attribution and descriptive information that you should fill in before you share the map. For example, the data attributions.

• Under Description, click on Edit. You can type the following: This map aims at providing support to spatially identify the potential sources of plastic pollution at a country level and use this information to determine national responsibilities and priorities for waste management policy.
• Under Terms of Use, add the following: This map uses information from different sources. To find the original source, please look at the section Credits (Attribution).
• Next to Credits (Attribution), click Edit and type: a) Eriksen, et al., (2014). Plastic pollution in the world's oceans: more than 5 trillion plastic pieces weighing over 250,000 tons afloat at sea; b) Ritchie and Roser (2018) Plastic Pollution; c) Meijer, et al., (2021). More than 1000 rivers account for 80% of global riverine plastic emissions into the ocean.
• Close the item page.

The online map created can be shared with anyone but first, we need to make sure that all the layers included, are shared publicly. In order to do that, we need to go to our Content's area within the project.

• Click on Home > Content.
• Look for the layer named Hot Spot Riverine Plastic Emissions_your_initials
• Click on top of it to access the details
• On the right side of the section Overview, look for Share and click
• Change the permisions to Everyone (public)
• Save

This process will allow anyone who access the map, be able to see all layers you are including in your online map, including the layer that resulted from the hotspot analysis you performed.

Now, let's go back to the map.

• Click on Content menu and there, you can click on your map.
• Click on Open in Map Viewer Classic

The fastest way to share a map is to share it with everyone and send an email that includes a link to your map. In the future, you could also embed the map in your blog, website or newspaper's website and create a web app or  StoryMaps  with additional text, videos, images, and web pages to enhance your map.

• In Map Viewer, click Share.
• In the Share window, check Everyone (public).
• You can Copy the link to the map so you can paste it into an email or Canvas site to share with your professor and others.
• Click Save.

• Make sure to save your work regularly and before closing the browser tab.
• If you would like to return to working on your map later, log back in to ArcGIS Online following the instructions at the beginning of this tutorial.
• Click on the top tab for Content. This will bring you to a page with all your personal ArcGIS Online maps, WebApps, surveys, StoryMaps, etc.
• Find your Web Map, World Plastic Pollution (First Name Last Name). Click on it. This will bring you to the item description that you edited earlier.
• To get back to working on your webmap, press Open in Map Viewer Classic. Now you can continue where you left off.