Vector Feature Editing

Feature editing adjusts the geometry and spatial relationships of features while preserving attributes or changing them as little as possible. Common tasks include correcting boundaries, moving features into position, breaking or merging line networks, splitting parcels by rules, and generating buffer areas.

Typical Scenarios

• Parcel or administrative boundary correction: move vertices, refine boundaries, and replace geometry.
• Road or utility line cleanup: extend, trim, split, intersect lines, and smooth lines.
• Land-use splitting and integration: interactive split, split by features, divide by equal distance, percentage, or area, and merge.
• Range analysis and derived geometry: create buffers, parallel copies, offsets, and points along lines.

Basic Workflow

1. Select the layer to edit.
2. Use a selection tool to select the target feature or features.
3. When continuous or seamless boundaries must be maintained, enable Topology and Snapping first.
4. Select the appropriate editing tool and complete the interaction. Undo or redo if needed.
5. Check the result for gaps, overlaps, and dangling points.

Enable Topology

Topology helps maintain spatial consistency between features during editing. For example, when adjacent parcels share a boundary, moving one boundary can make the other boundary follow it.

Steps:

1. Click the Topology drop-down button.
2. Enable Topological editing.
3. Adjust the topology tolerance as needed. A larger tolerance makes features more likely to snap or move together, but it may also introduce errors.

Enable Snapping

Snapping automatically snaps pointer placements to key positions of existing features, such as endpoints and edges. It improves editing accuracy and reduces topology errors.

• Common settings: snapping switch, snapping type such as endpoint or edge, XY tolerance in pixels, and tip content and color.
• Recommended use: enable Snapping before operations such as vertex editing, trim, split, polygon construction, and creating points along lines.

For a full example of Snapping in drawing workflows, see Vector Feature Drawing.

Tool Overview

Category	Tool	Main purpose	Common objects
Alignment and positioning	Move to	Move features accurately by coordinates, offsets, or direction and distance.	Point/line/polygon
Geometry editing	Edit vertices	Adjust line or polygon vertices to correct boundaries.	Line/polygon
Geometry editing	Replace geometry	Completely replace the original geometry with newly drawn geometry while preserving attributes.	Point/line/polygon
Geometry editing	Refine/extend/trim	Correct line or polygon shapes using reference lines or intersections.	Line/polygon
Geometry editing	Fillet	Create a tangent arc between intersecting lines.	Line
Geometry editing	Generalize, including simplify, smooth, and densify	Optimize geometry shape and vertex density.	Line/polygon
Splitting and reconstruction	Split/break	Split a line or polygon into multiple features.	Line/polygon
Splitting and reconstruction	Multipart to singlepart	Split multipart features into multiple singlepart features.	Line/polygon
Splitting and reconstruction	Divide	Split by equal distance, percentage, area, and other rules.	Line/polygon
Construction and derivation	Buffer	Generate distance-based polygon ranges, with different endpoint and join styles.	Point/line/polygon
Construction and derivation	Create points along line	Generate points along a line by point count, equal distance, or custom rules.	Line
Construction and derivation	Merge	Merge multiple features into one feature.	Line/polygon
Construction and derivation	Offset/parallel copy	Generate geometry at an offset distance from the original feature.	Line
Construction and derivation	Construct polygon	Construct closed polygons from boundary lines.	Line
Construction and derivation	Mirror/perpendicular copy	Copy features and apply symmetry or vertical offset.	Point/line/polygon
Line network processing	Line intersection	Split lines at explicit or implicit intersections.	Line
Geodetic features	Construct geodetic features	Create geodesics, rhumb lines, great elliptics, and similar features.	Line/polygon

Alignment

Move To

Move selected features accurately to a specified location. This is commonly used for correction, alignment, and distance-based translation.

• Absolute: enter target coordinates, based on the current project coordinate system and units.
• Delta: enter relative displacement values, based on the current project coordinate system and units.
• Direction/distance: enter an azimuth and distance.

Scale and Rotate Features

Scales and rotates selected features.

Geometry Editing

Edit Vertices

Adjusts, adds, or deletes vertices of line or polygon features. It is commonly used for boundary fine-tuning and topology repair.

Refine

Uses a refinement line or reference line to correct the boundary of a line or polygon.

• Line refinement: commonly used to replace part of a line with a more accurate segment.
• Polygon refinement: commonly used to correct polygon boundaries so they fit a reference line.

Replace Geometry

Completely replaces the geometry of the current feature with newly drawn geometry while keeping the feature attributes unchanged.

Continue Feature

Continues drawing from an existing feature. The newly drawn part inherits the attributes of the existing feature.

• Continue line feature: continue drawing from a line endpoint.
• Continue polygon feature: expand or shrink the boundary of an existing polygon.

Extend

Extends a line endpoint until it intersects the target feature. Only line feature extension is supported.

Trim

Cuts off an unwanted segment where a line intersects the target feature. Only line feature trimming is supported.

Fillet

Creates a tangent curve between two lines that intersect or would intersect if extended. It is commonly used to smooth road turns or utility line corners.

Generalize

Generalize is a group of geometry shape optimization tools mainly used for line and polygon boundary processing:

• Simplify: remove redundant vertices and reduce the vertex count.
• Smooth: make boundaries smoother while preserving the overall trend.
• Densify: add vertices along long boundaries to subdivide polylines more finely.

Common uses:

• Map production and rendering optimization: reduce the number of vertices in complex boundaries to improve frontend rendering performance.
• Geometry cleanup: smooth boundaries and reduce jagged edges.
• Computation preparation: prepare a more suitable vertex density for later operations such as buffer, offset, and polygon construction.

warning

Generalization changes geometry shapes. For data that must strictly preserve boundaries, such as cadastral or redline data, copy the layer first or generalize only display data.

Simplify

Simplify approximates the original line or boundary with fewer vertices. A common simplification principle in iXGIS is the Douglas-Peucker, or DP, algorithm:

• Use the two endpoints of a segment as the baseline and calculate the maximum perpendicular distance $d_{max}$ from intermediate points to the baseline.
• If $d_{max} \leq \varepsilon$, where $\varepsilon$ is the simplification tolerance, delete the intermediate points and keep only the endpoints.
• If $d_{max} > \varepsilon$, keep the point with the largest deviation and recursively process the two sub-polylines.

Here, $\varepsilon$ means the maximum allowed offset distance, and its unit is the same as the current data coordinate system.

Parameters:

Parameter	Meaning	Impact
Maximum allowed offset	Maximum allowed offset distance $\varepsilon$.	Larger values remove more vertices and make the shape simpler. Excessive values may cause obvious distortion.
Topology tolerance / Preserve topology, if available	Maintains topology consistency between features as much as possible during simplification.	Can reduce gaps and overlaps, but inappropriate tolerance values may introduce additional offsets.

Parameter recommendations:

• In a projected coordinate system, values are usually set in meters. Start with a small value and increase gradually while comparing results.
• In a geographic coordinate system, the unit is degrees. Avoid setting a large tolerance by intuition. Project the data to a suitable projected coordinate system before simplifying when possible.

Smooth

Smooth reduces sharp changes in a polyline and makes boundaries more continuous. Common smoothing principles apply filtering or interpolation to the vertex sequence:

• Moving average: replaces the current point with the average position of neighboring points to make the curve smoother.
• Gaussian smoothing: uses Gaussian weights to average neighboring points, emphasizing nearby points.
• Bezier: uses curve interpolation to generate a smoother curve shape.
• Exponential smoothing: uses exponential weights to smooth the sequence, balancing conformity to the original shape and smoothing strength.

Parameters:

Parameter	Meaning	Impact
Smoothing method	Moving average, Gaussian, Bezier, or exponential.	Different methods vary in corner preservation, overall offset, and smoothing strength.
Smoothing strength	Number of repeated smoothing passes applied to the result.	More passes create smoother results, but shape offset may become more obvious.

Notes:

• Smoothing may cause boundaries to shrink, expand, or shift, especially at sharp corners.
• If corner shapes need to be preserved, such as for regular building outlines, strong smoothing is not recommended.

Densify

Densify splits long segments into more short segments and increases vertex density without changing the overall shape. The principle is:

• Insert points along each segment by the maximum allowed spacing $L_{max}$ so the distance between adjacent vertices does not exceed $L_{max}$.
• For curved boundaries or cases requiring more uniform nodes, offset or angle constraints may be used if available in the interface.

Parameters:

Parameter, as shown in the interface	Meaning	Impact
Maximum distance	Maximum allowed distance $L_{max}$ between newly added vertices.	Smaller values create denser vertices and increase the vertex count.
Maximum offset	Limits the offset range of added points from the original boundary.	Helps avoid densification results that deviate too much from the original shape.
Angle threshold	Controls densification strategy near turns.	Affects whether corners are densified further and how strong the densification is.

Typical scenarios:

• Generate points at equal distances along a line, either by densifying first and then extracting points along the line, or by directly using Create points along line.
• Prepare enough vertices for later curve fitting, smoothing, or geometry transformation.

Splitting

Break

Break intersecting lines splits line features at intersections. It is commonly used to split a road network into road segments at intersections.

Split

• Interactive split: draw a split line to split a line or polygon.
• Split by features: use existing line features as split lines to split a line or polygon.

Multipart to Singlepart

Splits multipart features into singlepart features. The split features inherit attributes from the original feature.

Clip

Clip uses clip features, or a mask, to spatially extract target features and produce smaller, cleaner geometry results. It is commonly used to clip national or provincial data to a project area, administrative area, or study area.

Conceptually, Clip is a spatial overlay, or intersection, operation. The output usually retains the parts where target features overlap the clip features.

Typical scenarios:

• Clip basemap data such as roads, water systems, land use, and sensitive areas by a project boundary.
• Clip statistical areas by administrative areas such as provinces, cities, or counties.
• Improve map output by avoiding redundant features outside the study area.

In implementation, the process usually:

• Converts clip features to the coordinate system of target features before calculation.
• Preserves the output geometry type of the target features as much as possible: points remain points, lines remain lines, and polygons remain polygons.

Parameters:

Parameter, as shown in the interface	Meaning	Notes
Target features	Feature layer to be clipped.	Points, lines, and polygons are supported.
Clip features	Feature layer used to limit the area.	Polygons are usually recommended as clip features.
Clip method, if available	Selects which part of the geometry to keep.	Keep intersection, remove intersection, or keep both parts.
Buffer distance, if available	Buffers clip features before clipping.	Used to expand or shrink the boundary before clipping. Units depend on the coordinate system.
Output layer	Writes results to the layer where target features are located.	Overwrites existing content.

warning

Same-type clipping, such as line-by-line or point-by-point clipping, usually keeps only overlapping parts and can be easy to misunderstand. For beginners, polygon clip features are recommended.

Divide

Divides lines or polygons into multiple features by rules:

• Lines: equal parts, by distance, or by percentage.
• Polygons: proportional area, equal area, or equal width.

For polygons, choose the division method that matches the required result: proportional area, equal area, or equal width.

Construction

Create Points Along Line

Creates points along existing line features. It is commonly used for mileposts, sampling points, and equally spaced points.

• By point count: create points according to the specified number of points.
• By equal distance: create points at equal distances from the start or end of the line.

Merge

Merges multiple features into one feature. It is commonly used for parcel integration and line segment merging.

Buffer

Buffer generates a distance-based polygon range around point, line, or polygon features. It is commonly used for impact areas, safety setbacks, service coverage, and neighborhood analysis.

Typical scenarios:

• Environmental impact assessment or planning: 200 m impact zones along roads or 500 m impact zones along rivers.
• Safety setback: warning zones around hazardous sources.
• Service coverage: service radius for schools or hospitals.

A buffer can be understood as a distance expansion, or one-sided expansion, of input geometry. It returns all locations whose nearest distance to the input feature is no greater than $d$.

• Point buffer: usually a circle or an approximate circle.
• Line buffer: expands on both sides of the line and handles endpoints and corners.
• Polygon buffer: expands or shrinks polygon boundaries and may affect whether holes are preserved or disappear.

Parameters:

Parameter, as shown in the interface	Meaning	Impact
Buffer method	Planar or geodesic.	Planar is commonly used in projected coordinate systems. Geodesic is recommended in geographic coordinate systems.
Buffer distance	Buffer radius or expansion distance $d$.	Larger values create larger ranges. Units depend on the coordinate system.
Join style	Corner shape, such as round, miter, or bevel.	Determines whether corners form spikes or are truncated.
Miter limit	Limits spike extension length when used with miter joins.	Prevents excessively long spikes at acute angles.
Endpoint style	Buffer shape at line endpoints, such as round, flat, or square.	Determines whether the end extends and whether it is rounded.
Segments for approximate arcs, if available	Number of segments used to approximate circular arcs.	Larger values are smoother but create more complex geometry and slower computation.
One-sided buffer	Generates a buffer only on one side of a line feature.	Commonly used for road redlines and one-sided river impact zones.
Output layer	Select an existing layer or create a new layer.	Buffer feature type must match the feature type of the output layer.

Notes:

• Distance units: projected coordinate systems usually use meters. In geographic coordinate systems, using planar distance can cause obvious errors.
• Geometry quality: self-intersections and broken polygons may cause buffer failure or abnormal results. Repair geometry first if necessary.
• Acute-angle spikes: line or polygon buffers may create spikes at acute angles. Try adjusting the join style or miter limit.

Parallel Copy

Generates a new line that is parallel to the original line feature and keeps a fixed distance from it. It is used for road edges, parallel utility lines, and similar features.

Offset

Generates new vertices based on a feature or a drawn line.

Interactive offset and offset by features are supported:

• Interactive offset: draw a segment and create another segment or polyline based on the relative position, distance, and offset of that segment.
• Offset by features: select an existing feature and create another segment or polyline based on its relative position.

Both offset methods include the following parameters.

Feature parameters:

• Output layer: the layer where the new segment is constructed.
• Start at: recalibrates the start point of the feature by extending in the opposite direction of the segment direction. Only positive values are accepted.
• End at: recalibrates the endpoint of the feature by extending in the segment direction. Only positive values are accepted.

Offset parameters:

• Distance: position relative to the line start point.
• Offset: distance from one side of the line. Negative values are on the left side, and positive values are on the right side.
• Side: the side of the line on which to draw, either left or right.

The generated vertices form the new line segment.

warning

Resetting Start at and End at effectively stretches or compresses the original segment into the range between Start at and End at. This can deform the segment. Use with caution.

Construct Polygon

Constructs polygons from line features that can enclose areas. For boundaries that are not completely closed, a tolerance can help close them.

Perpendicular Copy

Copies selected features according to the copy count and shifts the Z value. The Z value of the nth copy is offset from the Z value of the (n-1)th copy.

Mirror

Creates a symmetric copy of selected features.

Line Intersection

Uses the intersection of two lines as a split point and creates new line segment features. Whether explicit or implicit intersections are used depends on the interface options.

Construct Geodetic Features

Creates geodetic features based on an ellipsoid. Common types include geodesics, rhumb lines, great elliptics, geodesic circles, and geodesic ellipses. Use cases and parameters depend on the interface.

Notes:

• Coordinate system and units: distance, area, direction, and other meanings and units depend on the current map coordinate system. Follow the interface prompts.
• Topology tolerance: a tolerance that is too large may introduce geometry offsets, while a tolerance that is too small may prevent linked movement or snapping.
• Snapping settings: XY tolerance is in pixels, so zoom level affects the apparent snapping range.
• Back up before editing: for critical data, export a backup or copy the layer before editing.

Geodesic

Definition: A geodesic is the shortest path between two points on the ellipsoid surface.

Characteristics

• Calculated from the Earth ellipsoid model.
• Not the same as a planar straight line.
• Usually appears as an arc in projections such as Web Mercator.
• Suitable for global-scale operations.

Typical applications

• Intercontinental flight routes.
• Global distance measurement.
• Transcontinental path analysis.

Mathematical meaning

It satisfies the minimum arc length condition:

s = minimum

Rhumb Line

A rhumb line, or loxodrome, is a curve on the Earth's surface that maintains a constant azimuth with all meridians.

Characteristics

• Constant heading angle.
• Appears as a straight line in a Mercator projection.
• Not the shortest path.

Typical applications

• Marine navigation.
• Constant-heading flight.

Key difference

• Geodesic: shortest path.
• Rhumb line: constant direction.

Great Elliptic

A great elliptic is the curve formed where the ellipsoid surface intersects the plane passing through the ellipsoid center and two surface points.

Characteristics

• Very close to a geodesic.
• Equivalent to a great circle in a spherical model.
• Slightly different from a geodesic on an ellipsoid.

Typical applications

• High-accuracy approximation for long-distance routes.
• Global-scale distance analysis.

Geodesic Circle

A geodesic circle is a curve made of all points on the ellipsoid surface that are at the same geodesic distance from a center point.

Characteristics

• Distance is calculated using ellipsoidal geodesic distance.
• Not the same as a planar buffer circle.
• Usually appears deformed in map projections.

Typical applications

• Communication coverage.
• Radar range.
• Spatial buffer analysis.

Geodesic Ellipse

A geodesic ellipse is constructed on the ellipsoid surface from major and minor axis lengths and a direction.

Common parameters

• Center point.
• Major axis length.
• Minor axis length.
• Direction angle, or azimuth.

Characteristics

• Constructed from geodesic distances.
• Not the same as a planar ellipse.
• Suitable for directional range representation.

Typical applications

• Error range representation.
• Uncertainty modeling.
• Search area analysis.