How to Create a Zone Map with a "Hole" for Exceptions

Defining Zones with Exceptions: How to Create a Zone with a "Hole"

Sometimes, geographic zones need to account for exceptions—specific areas where the general rules don’t apply. For example, you might set restrictions for a large area but want to allow certain exceptions, such as an industrial park or a recreational zone.

This can be achieved by creating a zone with a "hole" in a GeoJSON map. The "hole" acts as an exclusion area, allowing queries that match its location to bypass the larger zone’s rules and fall through to the next applicable zone or rule.

If you’re new to GeoJSON or mapping tools, don’t worry—we’ll guide you through the process step by step. Alternatively, our team is happy to create your custom zone map for you.

Why Use a Zone with a Hole?

Flexibility: Exclude specific areas within a larger restricted zone without creating multiple overlapping zones.
Efficiency: A single zone with a hole is easier to manage, modify, and query.
Accuracy: Clearly defines where rules apply and where they don’t, reducing confusion for residents, businesses, and public officials.

Having two zones—an outer zone with a seasonal policy and an inner zone with a different policy—provides a powerful tool for creating nuanced and flexible rules within a geographic area. Here's how this approach works and why it is beneficial:

Defining the Zones

Outer Zone:
- This represents the broader area, such as the boundaries of a city or district.
- It has a seasonal policy, meaning activities (e.g., burning) may be allowed during certain times of the year, depending on conditions like weather, air quality, or fire risk.
  Inner Zone:
- Nested within the outer zone, this smaller area follows a stricter policy, such as "no burning allowed ever."
- This can represent sensitive or high-risk areas, such as densely populated neighborhoods, industrial zones, or environmentally protected regions.

How This Configuration Creates Flexibility

Tailored Policies for Specific Needs:
- By establishing a no-burning zone within the larger seasonal-burning area, the rules align with the unique needs of each location. For example:
  - The outer zone might allow burning during safe conditions, such as in rural or low-density areas.
  - The inner zone, where risks are higher (e.g., near homes, schools, or businesses), is permanently restricted to ensure safety and compliance.
    Dynamic Control Without Complexity:
- Instead of creating numerous overlapping zones, this approach uses a clear hierarchy: the inner zone overrides the outer zone within its boundaries.
- This avoids confusion for residents and administrators while maintaining distinct policies for each zone.
  Clear Communication:
- Residents can easily understand where and when rules apply.
- For example:
  - "Burning is allowed in Zone A during the open season."
  - "Burning is not permitted in Zone B at any time, regardless of season."

Example Scenario

Imagine a city with a mix of rural and urban areas:

Outer Zone (City Limits):
Seasonal burning is allowed in safe conditions, such as during winter or when fire danger is low. This rule supports residents in rural areas who may need to burn debris for agricultural or maintenance purposes.
Inner Zone (No-Burn Area):
A densely populated downtown area or a nature preserve within the city limits is permanently excluded from burning to protect public safety, infrastructure, or the environment.

This setup creates flexibility, allowing the city to:

Balance rural and urban needs.
Adapt to seasonal risks without jeopardizing high-priority areas.
Ensure that exceptions are clearly defined and managed.

Why This Approach is Effective

Safety and Precision:
- Inner zones protect vulnerable areas while outer zones allow reasonable activity during safe periods.
Simplified Administration:
- Rules are easier to enforce because the hierarchy is clear—outer zones follow general policies, and inner zones enforce stricter exceptions.
Community Trust:
- Residents are more likely to comply when rules are specific, transparent, and aligned with the needs of their area.

This flexible zoning strategy offers the best of both worlds: enabling seasonal allowances in low-risk areas while protecting critical zones with stricter, permanent policies. It’s a smart way to manage complex geographic rules effectively.

How to Create a Zone with a Hole in GeoJSON

Option 1: Do It Yourself Using GeoJSON.io

GeoJSON.io is a simple, free tool that lets you draw geographic zones and define exception areas. Here’s how you can use it to create a zone with a hole:

Step 1: Open GeoJSON.io

Visit GeoJSON.io.
You’ll see a split screen with a map on the right and editable GeoJSON code on the left.

Step 2: Draw the Main Zone (Outer Boundary)

Click the Polygon Tool (hexagon icon) at the top of the screen.
Draw the outer boundary of your zone by clicking points on the map to create a polygon.
Close the shape by clicking on the starting point.
The GeoJSON code for your polygon will appear in the left-hand editor.

Step 3: Add the Exclusion Area (Inner Boundary)

Use the Polygon Tool to draw a smaller polygon inside the larger zone.
By default, GeoJSON.io creates this as a separate polygon. To make it a hole:
1. Copy the coordinates of the inner polygon.
2. Paste them into the coordinates section of the outer polygon as a second set of coordinates.
3. Ensure the first set defines the outer boundary and the second set defines the inner boundary (hole).

Here’s an example of GeoJSON code for a zone with a hole:

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "properties": {
        "zone_name": "Custom Zone with Exception"
      },
      "geometry": {
        "type": "Polygon",
        "coordinates": [
          [ // Outer boundary
            [100.0, 0.0], [101.0, 0.0], [101.0, 1.0], [100.0, 1.0], [100.0, 0.0]
          ],
          [ // Inner boundary (hole)
            [100.2, 0.2], [100.8, 0.2], [100.8, 0.8], [100.2, 0.8], [100.2, 0.2]
          ]
        ]
      }
    }
  ]
}

Step 4: Validate and Save

Use tools like GeoJSONLint to validate your GeoJSON.
Ensure the inner boundary visually subtracts from the outer zone on the map.
Save your GeoJSON file by clicking Save in GeoJSON.io.

Step 5: Use Your Zone Map

Upload your GeoJSON file to your system.
Queries will now correctly identify:
- Locations inside the outer boundary but outside the hole as part of the zone.
- Locations inside the hole as excluded and falling through to the next applicable zone or rule.

Option 2: Let Us Create Your Zone for You

If working with GeoJSON feels too technical, we’re here to help!

What We Need:

A map or description of the main zone.
A map or description of the areas to exclude (the hole).

This can include:

A drawing or screenshot with the areas marked.
GPS coordinates or a list of locations for inclusion/exclusion.

What We’ll Do:

Create a professionally formatted GeoJSON file, including the exclusion areas.
Validate the map to ensure accuracy and functionality.
Deliver the file to you and guide you on how to implement it in your system.

Final Thoughts

Creating a zone with a "hole" in GeoJSON provides flexibility and precision for defining geographic rules. Whether for fire restrictions, zoning regulations, or other use cases, this method ensures clear exceptions and streamlined management.

If you prefer to let us handle the details, contact us at support@publicfiresafety.com with your requirements, and we’ll take care of the rest.

Next Steps:

Try GeoJSON.io if you’d like to create your zone with a hole.
Reach out to us for assistance if needed—we’re happy to help you achieve the results you need.