Web GIS and Spatial Dashboards

What Is Web GIS?

Web GIS moves spatial data out of desktop software and onto the internet so that anyone with a browser can view, query, and interact with maps without installing specialized software. Platforms such as ArcGIS Online (Esri), CARTO, and Felt host your data on their servers, render tiles and feature layers, and serve them through secure HTTPS connections. The result is a living map that stakeholders can open on a laptop or phone, filter by attribute, and share with a single link.

Hosted Feature Layers

A hosted feature layer is a spatial dataset stored and served directly by the platform. When you upload a GeoJSON, CSV with coordinates, or Shapefile to ArcGIS Online, the platform converts it into a feature service — a REST endpoint that delivers features as JSON on demand. Unlike a static image tile, a feature layer supports querying ("show me only counties where population > 50,000"), editing, and pop-up interaction in the browser.

Key steps to create a hosted feature layer in ArcGIS Online:

1. Sign in to your free public account at arcgis.com.

2. Go to Content → New Item → Upload a local file and select your GeoJSON.

3. Choose Publish this file as a hosted feature layer.

4. After publishing, the item page shows a REST URL — this is your service endpoint.

If you are using an open alternative such as CARTO, the workflow is similar: connect a data source, let CARTO generate a tile layer and an API endpoint, then open the Map Viewer to style and share it.

Configuring Pop-Ups

Pop-ups are small information windows that appear when a user clicks a feature. A well-designed pop-up turns raw field names into readable labels and formats numbers clearly. In ArcGIS Online Map Viewer:

• Open Pop-up settings for the layer.
• Rename field aliases (e.g., change `med_hh_inc` to Median Household Income).
• Use the Format option to add currency symbols or round decimal places.
• Include at least three meaningful fields so the user can draw conclusions without leaving the map.

Poor pop-up design — such as showing every internal ID field — overwhelms users. Choose only the fields that answer the questions your audience is asking.

Graduated Color Renderers

A graduated color renderer (also called a choropleth style) maps a continuous numeric variable to a color ramp so that visual intensity communicates magnitude at a glance. Steps in ArcGIS Online Map Viewer:

1. Select the layer and open Styles.

2. Choose the numeric attribute (e.g., median income).

3. Select Counts and Amounts (Color) — this applies the graduated color method.

4. Pick a sequential color ramp (light-to-dark for low-to-high values) or a diverging ramp when your data has a meaningful midpoint.

5. Adjust the number of class breaks (5 is a common default) and the classification method (Natural Breaks, Quantile, or Equal Interval).

The choice of classification method changes what the map communicates. Quantile ensures equal numbers of features per class, which highlights relative rank. Natural Breaks minimizes within-class variance. Document your choice in the item summary so readers understand the representation.

Sharing a Web Map Publicly

A web map in ArcGIS Online is its own saved item — separate from the feature layer — that stores the map extent, basemap choice, layer styling, and pop-up configuration. To share:

1. Save the map with a descriptive title and summary.

2. Click Share → Everyone (public).

3. The platform warns you if the underlying layer is not also public; share the layer as well.

4. Copy the item URL. Test it by pasting into an incognito or private browser window to confirm it loads without sign-in.

Always test in incognito. A map that requires a login is not truly public and cannot be reviewed by your instructor or a future employer without an account.

Spatial Dashboards and Linked Widgets

A dashboard extends a web map by adding charts, gauges, lists, and filters on the same screen. ArcGIS Dashboards (included with a free public account in a limited form) and CARTO Builder both support linked widgets: when a user clicks or selects features on the map, connected charts update automatically to show statistics for only those selected features. This "linked view" pattern is foundational in visual analytics — it lets an end user filter spatially and see attribute summaries update in real time without any coding.

To add a linked bar or pie chart:

1. Open the Dashboard editor and add a Chart element.

2. Point it at the same hosted feature layer as your map.

3. Set the Map filter option so the chart respects the map's current selection.

4. Label axes clearly — a chart without axis labels is not publication-ready.

Data Accuracy and Professional Responsibility

Publishing spatial data publicly carries responsibility. Before sharing:

• Confirm your data source is properly cited and licensed for redistribution (many government open-data portals use CC0 or Open Government licenses — check the source).
• Remove or mask any personally identifiable information (PII) such as individual addresses linked to health or financial records.
• Do not publish data at a precision that could create privacy or security risks (e.g., exact GPS coordinates of private residences).

These practices align with responsible data stewardship principles that appear in the CompTIA Data+ and IBM Data Science Professional curricula.

Platform Accounts and Credentials

ArcGIS Online free public accounts do not require a credit card. Use your school email to register. Free accounts have storage limits and some advanced features (such as full ArcGIS Dashboards capabilities) may require an organizational account. If your institution provides an Esri Education site license, use that. Otherwise, CARTO free tier or Felt (felt.com) are fully functional alternatives for this exercise.