How to Turn Separate Curved Lines into One Correctly Filled Shape in Inkscape

A collection of curves can look enclosed without forming a connected outline. SVG, the format Inkscape uses, fills an open subpath as though a straight closing edge connected its last point to its first. Consequently, separate curved pieces can produce wedges or curved patches instead of filling the space you see between them. W3C: Painting—Fill Properties.

This also explains why applying a color is an unreliable closure test. A path can display a substantial fill while its endpoints remain disconnected. Your task is to establish the intended boundary, then inspect its appearance.

Consider two curves that form the upper and lower halves of an oval. Each curve alone can fill the area between its arc and an implied straight edge. Joining the corresponding ends turns those two pieces into the perimeter you actually want.

Save a working copy before changing the drawing. Identify every curve that belongs to the outside perimeter, and leave interior decorative lines out of the selection. For a single silhouette, you should be able to trace the intended boundary continuously back to your starting point.

Use this preparation check:

• Identify where each boundary curve should meet its neighbor.
• Decide whether each meeting point should be rounded or pointed.
• Look for extra lines crossing the interior.
• Check whether any objects are still geometric shapes rather than editable paths.

If a selected ellipse, rectangle, or other geometric shape shows shape-specific handles, use Path → Object to Path before editing its nodes. Conversion replaces the original shape controls with path editing, so retaining the working copy is useful. Curves already drawn as paths need no such conversion. Inkscape: Editing Nodes on a Geometrical Shape.

Keep the distinction between the curve and its visible outline in mind. A stroke is styled independently of the fill; its width and end caps affect what you see. Therefore, apparent contact between thick strokes is only a visual clue about the underlying geometry. Inkscape: Strokes.

For separate curves intended to become one continuous perimeter, start with Combine. It retains the pieces within a single path object. Those pieces remain independent subpaths until you connect them. Union serves a different task: merging the areas of existing shapes. Inkscape: Boolean Operations.

Starting situation	Appropriate approach
Open curves forming sections of one perimeter	Combine, then join corresponding endpoints
Closed shapes whose filled areas should merge	Union
An outer loop with a deliberate inner opening	Preserve separate closed subpaths and choose the appropriate fill rule

Select only the perimeter pieces with the Selector, then choose Path → Combine. Check the result before proceeding: having one selectable object does not mean every piece is connected. The manual explicitly distinguishes a compound path containing multiple subpaths from separate path objects. Inkscape: Boolean Operations.

Press N to activate the Node tool. Work around the perimeter one junction at a time:

1. Zoom into the first intended junction.
2. Select its two endpoint nodes.
3. Use Join selected nodes when the ends should become one node.
4. Use Join selected end nodes with a new segment when a connecting section should remain between them.
5. Repeat at each junction, including the final pair that closes the outline.

The merge command collapses selected nodes into one while attempting to preserve the path’s shape. The segment command connects endpoints. Select one intended pair at a time: the manual notes that joining a larger selection can connect the closest endpoints, which may differ from the connections you intended. Inkscape: Node Tool Options.

For the illustrative two-curve oval, select the matching left endpoints and join them, then select and join the matching right endpoints. Joining only one side leaves a continuous but open outline. This follows the path structure described by SVG: a path may contain connected segments, while a closed subpath returns to its starting point. W3C: Paths.

If selecting the pair is difficult, click one endpoint and Shift-click the other, or draw a small node-selection rectangle around them. Inkscape’s original Node tool documentation describes both selection methods. Inkscape Wiki: Node Tool Rewrite.

After connecting the boundary, inspect each junction for an unwanted corner or bulge. Joining establishes connectivity; the node type and handles determine how the outline flows through that connection.

Use a smooth node where the contour should flow continuously: its handles align through the node. Use a cusp node where you need a point or independently adjustable curvature on either side. A symmetric node additionally keeps both handles equally long, so choose it only when that constraint suits the contour. Inkscape: About Node Types.

Select the junction node and use the corresponding node-type control, then adjust its handles while watching both neighboring curves. Inspect one junction at a time so you can judge whether a local change improves the whole silhouette. Avoid converting every node to smooth when the design includes intentional corners.

Select the completed path and open Object → Fill and Stroke. In the Fill tab, choose flat color and select your color. In Stroke paint, retain an outline or choose the cross for no stroke. The dialog handles these paints separately. Inkscape: The Fill and Stroke Dialog.

If the result is unexpected, use this diagnostic sequence:

1. A diagonal edge cuts across the intended interior: revisit the corresponding endpoint connections; an open subpath may be filling against its implied closing edge.
2. An unexpected hole remains: inspect for an extra subpath, an overlapping loop, or a self-intersection before changing the fill rule.
3. The object appears invisible: check that Fill is a color rather than no paint, and inspect opacity.
4. A junction looks pointed: inspect that node’s type and handles.

Fill rules matter when paths intersect themselves or contain nested subpaths. With even-odd, a nested loop can create an opening regardless of its direction; nonzero also takes path direction into account. For a simple, non-intersecting closed outline, switching rules should not be necessary. Repair the boundary first, then address intentional openings. W3C: Winding Rule.

For invisible fills, check both the color’s alpha and the object’s overall opacity. SVG defines fill opacity separately, while Inkscape’s overall opacity control affects fill and stroke together. W3C: Fill Opacity, Inkscape: The Fill and Stroke Dialog.

Inspect every former junction with the Node tool, then review the silhouette at its intended viewing size. For the single outline covered here, the perimeter should be one closed loop without leftover open pieces. SVG distinguishes a closed subpath from an open one even when their endpoints occupy the same position, so merely moving two endpoints together is insufficient. W3C: The Closepath Command.

Finish by checking three things together: the boundary is connected, its curves have the intended corners and transitions, and the fill covers the intended interior. Once those agree, save the editable SVG so the silhouette remains straightforward to refine.

• Node Tool Options — Inkscape Beginners’ Guide
• Boolean Operations — Inkscape Beginners’ Guide
• Editing Nodes on a Geometrical Shape — Inkscape Beginners’ Guide
• Strokes — Inkscape Beginners’ Guide
• About Node Types — Inkscape Beginners’ Guide
• The Fill and Stroke Dialog — Inkscape Beginners’ Guide
• GSoC2009 Node Tool Rewrite — Inkscape Wiki
• Painting: Filling, Stroking and Marker Symbols — W3C SVG 2
• Paths — W3C SVG 2