Continuous, Hidden, Center, Phantom & Cutting Plane Lines

Technical drawings use different line patterns to communicate specific information. A line may represent a visible edge, a concealed feature, an axis, an alternate position or the location of an imaginary cut.

The five most common technical linetypes are:

Continuous lines
Hidden lines
Center lines
Phantom lines
Cutting plane lines

These patterns are widely used in mechanical drawings, architectural plans, civil drawings, manufacturing documents and CAD files.

Other standardized line types also exist. For example, short break lines and long break lines indicate that part of an object has been removed from the view or that a long object has been shortened graphically. However, this guide focuses on the five primary linetypes listed above.

Why Linetypes Matter in Technical Drawings

A technical drawing must communicate a large amount of information without relying on long written explanations.

Standard linetypes allow drafters, engineers, architects, manufacturers and contractors to understand the function of a line from its pattern and context.

They may indicate:

Visible boundaries
Invisible edges
Centers and axes
Lines of symmetry
Alternate positions
Adjacent parts
Movement paths
Section locations
Viewing directions

Correct linetype use improves drawing clarity, reduces interpretation errors and supports compliance with industry, company and project standards.

Linetype, Lineweight and Color

A linetype defines the pattern of a line.

Examples include:

Solid
Dashed
Long dash and short dash
Long dash and two short dashes

A lineweight defines the thickness of the line when it is displayed or plotted.

A color may control the on-screen appearance, plotting style or both, depending on the CAD configuration.

These properties work together but serve different purposes:

Linetype: identifies the pattern
Lineweight: creates visual hierarchy
Color: supports organization or plotting

For example, a continuous line may be thick when it represents a visible object outline and thin when it represents a dimension, leader or hatch boundary.

Comparison of Continuous, Hidden, Center, Phantom and Cutting Plane Linetypes

Characteristic	Continuous	Hidden	Center	Phantom	Cutting Plane
Typical pattern	Solid	Short dashes	Long dash and short dash	Long dash and two short dashes	Heavy segmented or chain line
Main meaning	Visible geometry	Concealed geometry	Axis, center or symmetry	Alternate position or adjacent feature	Location and direction of a section
Represents a physical edge	Usually	Yes, but not visible	No	Sometimes	No
Commonly shows movement	No	No	No	Yes	No
Commonly includes arrows	No	No	No	No	Yes
Typical applications	Outlines, walls, borders	Internal holes, concealed edges	Shafts, holes, circular features	Moving parts, alternate positions	Section views and building sections

What Is a Continuous Linetype?

A continuous linetype is a solid, uninterrupted line with no gaps or repeating pattern.

It is the most common linetype in technical drawings.

What Continuous Lines Represent

Continuous lines usually show geometry that is visible from the current viewing direction.

They may represent:

Visible object edges
Visible contours
Physical boundaries
Wall outlines
Structural elements
Equipment outlines
Drawing borders
Dimension lines
Extension lines
Leaders
Hatch boundaries

The meaning of a continuous line also depends on its lineweight.

Continuous Lineweight Hierarchy

A thick continuous line commonly represents:

Visible object outlines
Major boundaries
Sectioned object edges
Important structural elements

A thin continuous line may represent:

Dimensions
Extension lines
Leaders
Hatching
Construction geometry
Projection lines

An extra-thick continuous line may be used for:

Drawing borders
Match lines
Major section boundaries
Special emphasis

Common Uses of Continuous Lines

In mechanical drawings, continuous lines show the visible outlines of parts and assemblies.

In architectural drawings, they may show:

Walls
Doors
Windows
Fixtures
Structural components
Room boundaries

In civil drawings, they may represent:

Road edges
Curbs
Property boundaries
Pipelines
Site limits

Continuous Linetype in AutoCAD

AutoCAD includes the standard CONTINUOUS linetype.

Objects may use it directly or inherit it from their layers.

Common property settings include:

ByLayer
ByBlock
Continuous
A loaded custom or standard linetype

When an object is set to ByLayer, it inherits the linetype assigned to its layer.

When it is set to ByBlock, its appearance may depend on the block reference in which it is used.

When Continuous is assigned directly to an object, the object remains solid even if its layer uses another linetype.

Because a continuous line has no spaces or dashes, changing LTSCALE does not normally produce a visible change.

What Is a Hidden Linetype?

A hidden line normally consists of short, evenly spaced dashes.

It represents an edge or feature that exists but cannot be seen directly from the current viewing direction.

What Hidden Lines Represent

Hidden lines may show:

Internal holes
Blind holes
Internal bores
Recesses
Slots
Back edges
Concealed components
Underground utilities
Features located behind another object

They allow the reader to understand geometry that is not visible in the current view.

Hidden Lines in Mechanical Drawings

In mechanical drafting, hidden lines commonly represent:

Internal cavities
Counterbores
Slots
Recesses
Holes passing through a part
Features located on the opposite side of a component

For example, the sides of an internal hole may appear as two dashed lines in a side view.

However, hidden lines should not be overused. When internal geometry becomes difficult to read, a section view is often clearer.

Hidden Lines in Architectural and Civil Drawings

In architectural drawings, dashed or hidden-style lines may represent:

Objects above the plan cutting plane
Objects below the floor
Roof overhangs
Upper cabinets
Concealed beams
Foundations
Hidden structural components

In civil drawings, they may show:

Underground pipes
Buried utilities
Drainage systems
Culverts
Subsurface structures

The exact meaning should always be confirmed through the drawing legend, layer name or project CAD standard.

Hidden Line vs. Generic Dashed Line

The term dashed line describes the appearance of a line.

The term hidden line describes its technical meaning.

Not every dashed line represents hidden geometry.

A dashed line may also indicate:

Demolition work
Existing conditions
Future construction
Property setbacks
Overhead elements
Survey boundaries
Utility routes

Context is therefore essential.

Hidden Linetypes in AutoCAD

Common AutoCAD hidden linetypes include:

HIDDEN
HIDDEN2
HIDDENX2

These linetypes use the same general dash pattern at different predefined sizes.

HIDDEN2 uses a smaller pattern.
HIDDENX2 uses a larger pattern.

The correct version depends on the drawing units, object size and intended plot scale.

What Is a Center Linetype?

A center linetype usually consists of a repeating long dash followed by a short dash.

It identifies the center, axis or symmetrical relationship of an object.

What Center Lines Represent

Center lines may show:

Axes of cylindrical objects
Centers of circles and arcs
Lines of symmetry
Rotation axes
Bolt circle centers
Alignment paths
Structural grids

A center line normally does not represent a physical edge. It represents reference geometry.

Common Uses of Center Lines

Center lines are commonly used for:

Holes
Shafts
Cylinders
Pipes
Bearings
Circular plates
Rotating components
Symmetrical mechanical parts
Circular patterns

A shaft may have a centerline along its axis.

A circular hole may have two intersecting centerlines.

A symmetrical object may have a centerline dividing it into equal halves.

Centerline vs. Centermark

A centerline identifies:

An axis
A line of symmetry
The alignment between features
The center between two parallel edges

A centermark identifies:

The center of a circle
The center of an arc
The location of a circular feature

A centermark usually appears as a small cross or pair of intersecting lines.

How Far Should a Centerline Extend?

A centerline normally extends slightly beyond the visible boundary of the object.

This makes it easier to distinguish from visible geometry.

The exact extension depends on:

Drawing scale
Object size
Drafting standard
Company requirements

The main objective is to maintain a clear and consistent appearance.

Center Linetypes in AutoCAD

Common AutoCAD center linetypes include:

CENTER
CENTER2
CENTERX2

AutoCAD also includes dedicated commands:

CENTERLINE
CENTERMARK

The CENTERLINE command creates a centerline between suitable linear or parallel objects.

The CENTERMARK command creates an associative center mark for a circle or arc.

Associative center objects may update when the related geometry changes.

What Is a Phantom Linetype?

A phantom line normally consists of one long dash followed by two short dashes.

It is used to show alternate positions, moving parts, adjacent components or reference geometry.

What Phantom Lines Represent

Phantom lines may indicate:

Alternate positions of moving parts
Movement ranges
Adjacent components
Repeated details
Reference geometry
Future positions
Features located outside the primary view

Unlike hidden lines, phantom lines do not normally indicate concealed edges.

They represent geometry that is real, possible, adjacent or shown for reference.

Phantom Lines in Mechanical Drawings

In mechanical drawings, phantom lines may show:

A lever in an alternate position
A cover in the open position
A moving part at the end of its travel
An adjacent assembly
A repeated feature
The path of a component

For example, a machine guard may appear with a continuous outline in its closed position and a phantom outline in its open position.

Phantom Lines in Architectural Drawings

In architectural drawings, phantom-style lines may be used for:

Alternate equipment positions
Door or panel movement
Adjacent structures
Future construction
Overhead elements
Reference features

However, architectural offices may use similar patterns differently. The drawing legend and office CAD standard should define the intended meaning.

Phantom Line vs. Center Line

A center line normally follows this pattern:

Long dash
Short dash
Long dash
Short dash

A phantom line normally follows this pattern:

Long dash
Short dash
Short dash
Long dash
Short dash
Short dash

Their meanings are also different:

Center line: axis, center or symmetry
Phantom line: alternate position, movement or adjacent geometry

The two patterns must remain clearly distinguishable at the final plot scale.

Phantom Linetypes in AutoCAD

Common AutoCAD phantom linetypes include:

PHANTOM
PHANTOM2
PHANTOMX2

These definitions use the same basic pattern at different sizes.

What Is a Cutting Plane Linetype?

A cutting plane line shows where an imaginary cut passes through an object, assembly or building.

The cut creates a section view, which reveals internal geometry that cannot be understood clearly from exterior views alone.

What Cutting Plane Lines Communicate

A cutting plane indication normally shows:

The location of the cut
The direction of observation
The section identification
The connection between the original view and the resulting section

A cutting plane may pass directly through an object or change direction to include several important features.

Main Components of a Cutting Plane Indication

A complete cutting plane symbol may include:

A thick or emphasized line
A segmented or chain pattern
Directional arrows
Section labels
Reference numbers
Bends or offsets

Typical section labels include:

A–A
B–B
C–C

The arrows indicate the direction from which the section is viewed.

Cutting Plane Lines in Mechanical Drawings

In mechanical drawings, cutting planes help reveal:

Internal cavities
Holes
Wall thicknesses
Internal channels
Fasteners
Shafts and bearings
Assembly relationships

A section view can often replace several hidden lines and make the drawing easier to understand.

Cutting Plane Lines in Architectural Drawings

In architectural drawings, cutting plane lines identify:

Building sections
Wall sections
Stair sections
Interior sections
Structural sections
Detail sections

The cutting plane is usually placed on a floor plan and connected to a corresponding sectional drawing.

ASME vs. ISO Cutting Plane Conventions

The exact appearance of a cutting plane line depends on the applicable standard.

Under ASME conventions, especially in North American mechanical drafting, cutting plane lines are often shown as a thick phantom-style line with arrows at the ends.

The pattern may therefore resemble:

One long dash
Two short dashes
One long dash

Under ISO conventions, a cutting plane is commonly shown with a thin chain line similar to a centerline, but with thickened ends and thick segments at changes of direction.

This distinction is important:

ASME: commonly uses a heavy phantom-style pattern
ISO: commonly uses a thin chain line with emphasized ends and direction changes

The project or company standard should always take priority.

Cutting Plane Line vs. Section Hatching

A cutting plane line identifies where the object is cut and the direction of viewing.

Section hatching, also called section lining, appears on the surfaces exposed by the cut.

Therefore:

Cutting plane line: defines the location of the section
Section hatching: represents the cut surfaces or material

These are separate drafting elements.

Cutting Plane Linetypes in AutoCAD

A cutting plane is usually more than a basic linetype.

It may include:

A heavy line or polyline
Arrows
Section labels
Annotation blocks
View references

In an ASME-based workflow, users may apply the PHANTOM linetype with an appropriate heavy lineweight.

In an ISO-based workflow, users may use a CENTER-style chain pattern with thicker segments at the ends and bends.

Many offices create complete section symbols using:

Blocks
Dynamic blocks
Multileaders
Tool palettes
Specialized mechanical or architectural tools

This approach is generally clearer than using a patterned line without arrows or labels.

How These Linetypes Work Together

A single technical drawing may use all five linetypes.

Consider a mechanical component with an internal hole and a movable lever:

Continuous lines show the visible outer shape.
Hidden lines show the internal hole.
Center lines identify the axis of the hole.
Phantom lines show the lever in an alternate position.
A cutting plane line identifies where a section view is created.

In an architectural floor plan:

Continuous lines show walls and visible fixtures.
Hidden or dashed lines show overhead or concealed features.
Center lines identify grids or circular geometry.
Phantom lines may show adjacent or future elements.
Cutting plane lines identify building and wall sections.

The meaning of each line depends on its pattern, lineweight, layer, annotation and drawing context.

Linetype Standards and Conventions

Technical linetypes are defined by recognized drafting systems and standards.

Common references include:

ASME
ANSI
ISO
BS
DIN
National CAD standards
Company drafting standards
Client-specific standards

Standards such as ISO 128 and ASME Y14.2 define general conventions for line types and their applications.

However, exact patterns and meanings may vary according to:

Industry
Country
Discipline
Project type
Client requirements
Company practices
Drawing scale

A dashed line in a mechanical drawing may indicate a hidden edge, while a similar pattern in an architectural drawing may indicate demolition, overhead geometry or future work.

Before interpreting a line, check:

The drawing legend
The layer name
The CAD standards manual
The project template
Client requirements
Existing project drawings

How Linetype Scale Works in AutoCAD

Dashed and chain linetypes must be displayed at an appropriate scale.

If the scale is incorrect, a hidden, center or phantom line may appear continuous, excessively compressed or widely spaced.

Important AutoCAD Linetype Scale Variables

LTSCALE

LTSCALE controls the global linetype scale for the drawing.

Increasing the value makes dash patterns larger.

Decreasing the value makes them smaller.

CELTSCALE

CELTSCALE controls the linetype scale assigned to newly created objects.

It works in combination with the global LTSCALE value.

Individual objects may also have their own linetype scale overrides.

PSLTSCALE

PSLTSCALE controls the display of linetypes in paper space viewports.

It helps maintain a consistent plotted appearance across viewports with different scales.

MSLTSCALE

MSLTSCALE affects how linetypes appear in model space when annotation scaling is involved.

These variables interact with:

Drawing units
Object scale
Viewport scale
Linetype definition
Plot scale

Metric vs. Imperial Linetype Definitions

AutoCAD includes separate linetype definition files for metric and imperial drawings.

Typical files include:

acad.lin for imperial definitions
acadiso.lin for metric definitions

Using an imperial linetype definition in a metric drawing, or the reverse, can produce a scale difference of approximately 25.4.

This may cause dash patterns to appear much too large or much too small.

MEASUREMENT and MEASUREINIT

The MEASUREMENT system variable indicates whether the current drawing uses imperial or metric defaults.

Typical values are:

0 for imperial
1 for metric

This setting influences which hatch and linetype definition files AutoCAD uses by default.

The MEASUREINIT system variable controls the initial measurement setting for newly created drawings that do not use an explicit template.

In practical terms:

Imperial drawings typically load definitions from acad.lin.
Metric drawings typically load definitions from acadiso.lin.

Checking MEASUREMENT and MEASUREINIT can help prevent inconsistent linetype scaling and unexpected 25.4 conversion issues.

Regenerating the Drawing

After changing linetype settings, use:

REGEN
REGENALL

You may also need to:

Refresh viewports
Change the zoom level
Reopen the layout
Check the plot preview

The final plotted result is more important than the temporary on-screen appearance.

Common Linetype Mistakes

Confusing Hidden and Center Lines

A hidden line uses short dashes and represents concealed geometry.

A center line uses alternating long and short dashes and represents an axis, center or line of symmetry.

Using Phantom as a Generic Dashed Linetype

A phantom line has a recognized technical meaning.

Using it for arbitrary boundaries or notes may cause readers to interpret it as an alternate position, moving part or adjacent feature.

Drawing a Cutting Plane Without Arrows

A cutting plane line shows the location of the cut, but the arrows show the viewing direction.

Without arrows, the section orientation may be unclear.

Relying Only on Color

Color should not be the only method used to identify technical information.

Colors may change because of:

Monochrome plotting
CTB or STB settings
Printer configuration
File conversion
Software differences
User display settings

Use linetype, lineweight, layer name and annotation together.

Assigning Linetypes Directly to Objects

Direct linetype overrides make drawings harder to manage.

When practical, assign linetypes to layers and keep objects set to ByLayer.

This allows global changes to be made through the Layer Properties Manager.

Best Practices for Technical Linetypes

Assign linetypes through properly named layers.
Use ByLayer whenever practical.
Follow the applicable drafting standard.
Maintain a clear lineweight hierarchy.
Avoid unnecessary hidden lines.
Use section views for complex internal geometry.
Keep center and phantom patterns visually distinct.
Use arrows and labels for cutting planes.
Check linetypes at the intended plot scale.
Verify both model space and paper space display.
Use metric definitions for metric drawings.
Use imperial definitions for imperial drawings.
Check MEASUREMENT when linetype sizes are inconsistent.
Include a legend for nonstandard patterns.
Avoid relying only on color.
Review the plot preview before issuing the drawing.

AutoCAD Linetype Troubleshooting

Why Does a Hidden Line Look Continuous?

A hidden line may appear solid when:

LTSCALE is too small
The object linetype scale is too small
The object is too short to display a full dash pattern
The wrong metric or imperial definition was loaded
Viewport linetype scaling is inconsistent
The drawing has not been regenerated

Check:

LTSCALE
CELTSCALE
The object Linetype Scale property
PSLTSCALE
MSLTSCALE
MEASUREMENT
The loaded .lin file

Then run REGENALL and verify the result in plot preview.

Why Do Linetypes Look Different in Two Viewports?

Different viewport scales may change the apparent size of dash patterns.

Check PSLTSCALE and confirm that the layout is regenerated.

Also verify that objects do not have inconsistent individual linetype scale overrides.

Why Are Metric Linetypes Too Large or Too Small?

The drawing may be using an imperial linetype definition such as acad.lin instead of the metric acadiso.lin file.

Check MEASUREMENT and reload the correct linetype definition.

A mismatch between imperial and metric patterns commonly creates a factor close to 25.4.

Conclusion

The five main technical linetypes have distinct meanings:

Continuous lines represent visible geometry.
Hidden lines represent concealed edges and features.
Center lines identify axes, centers and symmetry.
Phantom lines show alternate positions, movement or adjacent geometry.
Cutting plane lines identify the location and viewing direction of a section.

Their correct use improves drawing readability, technical communication and standards compliance.

However, a line should not be interpreted from its pattern alone. Always consider its lineweight, layer, annotation, drawing discipline, project legend and applicable drafting standard.