To remove hairline gaps between adjacent shapes in Affinity on Mac, first check whether the edges actually meet. Then merge matching fills, overlap opaque shapes, or adjust antialiasing for raster output. Export settings alone cannot repair missing geometry.

This guide uses the current Affinity desktop interface. Its task is to produce a finished graphic without unwanted seams while preserving vectors where practical. The diagnostic sequence below combines documented controls with explicitly identified tests; it does not assume every thin line has the same cause.

Is the hairline a real gap or an edge-rendering problem?

Affinity explains that antialiasing smooths edges by adding semitransparent pixels between an object and its background. Consequently, a pale boundary can involve edge coverage even when the intended shapes meet. That is a reason to investigate geometry and rendering separately, rather than immediately enlarging every object. Layer blend options

Save a working copy, then compare the affected boundary in three places: the document, the export preview, and the exported file opened in its intended viewing app. Keep the export area and output dimensions consistent. Affinity’s Export dialog provides a zoomable preview; on Mac, press ⌘1 within that preview for 100%, ⌘2 for 200%, or ⌘3 for 400%. Export dialog

Use these observations as diagnostic clues, not conclusive proofs:

Observation Next useful check
The boundary appears open in the source artwork Inspect the shapes’ positions and dimensions.
The shapes meet numerically, but a pale edge remains Test a union or controlled overlap on a copy.
A PNG contains the line at its intended dimensions Correct the artwork or Affinity’s raster rendering before delivery.
A PDF or SVG looks different between viewing apps or zoom levels Compare a raster export before changing the geometry.

For two unrotated rectangles, open Window > General > Transform. Select the top-left anchor point and compare the left rectangle’s X + W with the right rectangle’s X. Also check their vertical positions and heights. The panel supports exact position and size values, and its anchor determines how those values are interpreted. Bounding-box arithmetic is useful for rectangles; it does not establish that two curved edges coincide. Transform panel

For example, a rectangle at X = 0 px with W = 120 px ends at 120 px. A second rectangle beginning at X = 120.25 px leaves a 0.25 px geometric gap. These are illustrative values, not measurements from an Affinity test. Correct that mismatch before experimenting with export quality.

Which correction preserves the artwork you need?

Choose a correction according to the relationship between the shapes. The following decision aid is derived from Affinity’s documented Boolean, transform, and antialiasing controls; it is not a promise that one setting removes every seam.

Artwork requirement First correction to try Condition or tradeoff
Touching shapes should form one continuous fill Add them into one shape or compound Add uses the lowest object’s color.
Different opaque colors must remain distinct Extend the lower shape beneath the upper shape Check that the overlap preserves the visible boundary.
A small raster graphic needs hard edges Test Antialiasing: Force Off Curves and diagonals may become jagged.
A finished appearance matters more than vector structure Export a checked raster result Resolution becomes part of the deliverable.

Join shapes that should share one fill

If adjacent pieces represent one continuous solid region, removing the internal boundary is a direct geometric solution. Affinity’s Add operation combines the selected areas and uses the lowest object’s color. A compound keeps its component objects available for later editing. Creating compounds

  1. In the Vector Studio, select the relevant shapes.
  2. Choose Vector > Geometry > Add, or click Add on the toolbar, to create a compound.
  3. Check the resulting fill and outer outline.
  4. Export again and inspect the former join.

For a permanent Boolean result, the current desktop help documents holding ⌥ Option while choosing Add on the Vector Studio toolbar. Keep the editable source before doing this. Add combines existing areas; it does not invent a bridge across genuinely separated shapes. Joining with Booleans

Use this approach for compatible fills. Combining differently colored pieces changes the design because Add adopts the lowest object’s color. A simple group also does not perform the documented Boolean union.

Overlap different opaque fills deliberately

When two colors must stay separate, a useful construction is to let the lower shape continue underneath the upper one. This is a geometric workaround inferred from covering the background beneath the join. It is appropriate to test with opaque fills; transparent fills, blend modes, or effects can make the overlap visibly different.

Consider an illustrative pair of unrotated, unstroked rectangles. Rectangle A is below B, starts at X = 0 px, and is 120 px wide. B starts at X = 120 px. To test a 1 px overlap while preserving A’s left edge, select A, choose the top-left Transform anchor, disable the width–height Link, and change W to 121 px. Affinity documents these anchor, width, and independent-sizing controls. Transform panel

The 1 px amount is a trial value, not an Affinity recommendation. Inspect the actual export and use only enough overlap to solve the visible problem. For irregular artwork, extend only the hidden boundary rather than scaling the entire object. Check the outer silhouette, corners, and any intentional openings afterward.

How do you adjust antialiasing for a raster export?

Affinity provides a documented layer control for antialiasing. In the Layers panel, select an affected shape, click Blend Options, and change Antialiasing to Force Off. Repeat for the other affected shape and compare an export at the intended dimensions. Inherit adopts the parent layer’s setting; Force On and Force Off override inheritance. Layer blend options

Disabling antialiasing removes edge smoothing, so inspect the entire shape. A straight join may improve while a rounded corner becomes visibly stepped. Treat Force Off as an output-specific test for hard-edged graphics, rather than a default for every illustration.

The same dialog includes Coverage Map, which controls the antialiasing ramp and edge strength. Affinity documents editing its profile and resetting it. The help does not supply a universal seam-removal curve, so avoid copying arbitrary profile coordinates as a guaranteed fix. Start with the simpler Force Off comparison and restore the original setting if the tradeoff is unacceptable. Layer blend options

For axis-aligned raster artwork, also check pixel placement. Go to View > Snapping and enable Force Pixel Alignment. Affinity says this snaps objects, nodes, and handles to whole pixels as they are created, moved, or modified. Other snapping targets can still produce positions off the pixel grid. Force Pixel Alignment

Move By Whole Pixels has a different purpose: it can preserve an existing fractional-pixel position while moving an object by whole-pixel distances. Enabling it alone therefore does not establish that an edge is pixel-aligned. Recheck the coordinates, and remember that pixel alignment does not eliminate smoothing along every curve or diagonal. Force Pixel Alignment

What do PDF and SVG export settings actually guarantee?

For controlled comparisons, use File > Export > Export, select the required preset, and inspect the File and Advanced settings. Choose the whole document or the relevant artboard consistently. Selection Area includes overlapping unselected layers; Selection Only excludes them. That distinction matters if your seam correction relies on an underlying shape. Export dialog

Affinity documents three Rasterize choices for PDF, SVG, and EPS:

  • Nothing: exports without rasterizing design elements; unsupported elements are omitted.
  • Unsupported properties: rasterizes only unsupported elements.
  • Everything: rasterizes all elements to preserve the original appearance.

These are format-conversion choices, not geometry-repair commands. In particular, Nothing can remove unsupported content and should not be treated as a universal quality improvement. Export Settings

For a vector deliverable, first correct actual gaps and use unions or overlaps where the design permits. Then inspect the exported PDF or SVG in the destination app. The documented layer antialiasing controls do not provide an explicit guarantee that every external viewer will reproduce Affinity’s coverage settings. Avoid promising that Force Off in the source will suppress seams in every vector viewer.

For a raster delivery, export PNG at the intended width and height and inspect that file. Affinity documents image dimensions separately from Raster DPI, which controls the resolution of effects rasterized during applicable vector-format exports. Increasing Raster DPI does not close a geometric gap or alter a retained vector boundary. Export Settings

If the delivery must be a PDF but vector structure is optional, PDF (flatten) is a documented starting point: its preset uses Rasterize: Everything and the document’s raster resolution. This can carry a checked raster appearance into PDF, but rasterization will also preserve a seam already visible in Affinity’s rendered result. Fix and inspect that appearance first. Compare PDF export presets

Review Downsample images and Allow JPEG compression when testing a rasterized PDF. Affinity documents that these can reduce raster resolution and compress rasterized elements. Disabling them during comparison helps you assess the boundary without those additional changes; it does not itself repair the join. Export Settings

How do you confirm the seam is gone?

Export after changing one factor at a time. Check the formerly affected boundary at the intended display size, then enlarge it to inspect corners and transitions. For transparent graphics, compare against both a light and a dark background. For vector delivery, check the actual PDF or SVG in the app where it will be used; keep a raster comparison available to help identify rendering differences.

Finish with the correction that preserves the required appearance and structure: join continuous fills, extend opaque lower shapes beneath adjoining colors, or use a verified raster output when that meets the delivery requirement. Keep the editable Affinity document so future size or color changes can be checked again.

Sources