Adding Features - Polyline/Polygon Snapping

📝 Overview

Polyline/Polygon snapping allows you to align new geometry with an OS feature or an existing overlay graphic.

To begin:

1. From the Add menu, select the graphic type you wish to add (Polyline or Polygon).

2. Step through the geometry creation process. Various dialogue boxes will appear — you can use the mouse to select options, or keyboard shortcut keys shown by underlined letters.

   • Shortcut keys can also be seen by hovering over the status bar (see The GGP Environment for details).

3. Position the cursor over the feature you want to snap to and right-click.

4. From the menu, select Snap.

5. The selected feature will be highlighted and the Select Snap Point dialogue box will appear.

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🎯 Select Snap Point Options

If provided, choose between:

• Calculated point

• Node point

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📍 Snapping to a Point

1. In the Select Snap Point dialogue:

   • Uncheck Part Line.

   • Uncheck Include all of line/polygon.

2. Click [OK].

3. The polyline/polygon will then “rubber band” around the fixed point where you snapped to the line.

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📏 Snapping to a Section

1. In the Select Snap Point dialogue:

   • Leave Part Line checked.

   • Click [OK].

2. Position the cursor along the chosen feature at the required section length and left-click.

3. The Select End Point dialogue appears with two options:

   • Use nearest node point (default) → Finds the nearest node point to where you clicked.

   • Use nearest calculated point → Finds a calculated point along the feature.

You can select using the mouse or keyboard shortcuts.

• The required section is highlighted.

• The cursor continues to “rubber band” at the end point until you save or cancel.

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🔄 Snapping to a Whole Feature

1. Position the cursor at the start point of the feature.

2. Right-click and select Snap.

3. In the Select Snap Point dialogue:

   • Leave Part Line checked.

   • Tick Include all of line/polygon.

   • Click [OK].

4. The entire feature is highlighted.

   • The cursor rubber bands from the end point to continue.

   • The feature can be reversed, allowing you to continue from your chosen start point.

💡 Example: Useful when building “school-to-home” lines from existing features radiating out from a school.

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✅ Accept Line Segment

When snapping to an enclosed OS feature or overlay polygon, the Accept line segment dialogue may appear.

• Click [OK] to accept the highlighted section.

• Click Reverse to swap to the opposite section, then [OK] to confirm.

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🌍 Snapping Outside the Current Viewport

If the snap end point lies outside the visible map area:

• The viewport will scroll automatically to centre on the end point.

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➡️ Continue Snapping Option

GGP can search for connected lines from the end of the highlighted line.

• If found, you are prompted: “Click [Yes] to snap to next feature.”

• Selecting [Yes] reopens the Select Snap Point dialogue.

• The initial snap point is set to the end of the currently highlighted line.

• GGP highlights the next available feature.

  • Use [Previous feature] and [Next feature] buttons to cycle through candidates.

  • Select the feature you require.

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⚠️ Warning: Always check your selected snap point and options carefully, as continuing or reversing a snap can extend geometry further than intended.