C3d Parcels

Civil 3D Parcels

Use this skill when creating, modifying, or querying parcels and sites, working with parcel segments and topology, or configuring parcel styles and labels.

Sites

Sites are containers that enforce topology between parcels and alignments. All parcels must belong to a site.

CivilDocument doc = CivilApplication.ActiveDocument;

// Get all sites
ObjectIdCollection siteIds = doc.GetSiteIds();
foreach (ObjectId siteId in siteIds)
{
    Site site = ts.GetObject(siteId, OpenMode.ForRead) as Site;
    ed.WriteMessage("Site: {0}\n", site.Name);

    // Get parcels in this site
    ObjectIdCollection parcelIds = site.GetParcelIds();
    ed.WriteMessage("  Parcels: {0}\n", parcelIds.Count);

    // Get alignments in this site
    ObjectIdCollection alignIds = site.GetAlignmentIds();
    ed.WriteMessage("  Alignments: {0}\n", alignIds.Count);

    // Get feature lines in this site
    ObjectIdCollection flIds = site.GetFeatureLineIds();
    ed.WriteMessage("  Feature Lines: {0}\n", flIds.Count);
}

Creating a Site

// Create a new site by name
ObjectId siteId = Site.Create(doc, "My Subdivision");
Site site = ts.GetObject(siteId, OpenMode.ForWrite) as Site;
site.Description = "Phase 1 residential lots";

Accessing Parcels

// Through a site
Site site = ts.GetObject(siteId, OpenMode.ForRead) as Site;
ObjectIdCollection parcelIds = site.GetParcelIds();

foreach (ObjectId parcelId in parcelIds)
{
    Parcel parcel = ts.GetObject(parcelId, OpenMode.ForRead) as Parcel;
    ed.WriteMessage("Parcel: {0}, Number: {1}, Area: {2:F2}\n",
        parcel.Name, parcel.Number, parcel.Area);
}

Parcel Properties

Parcel parcel = ts.GetObject(parcelId, OpenMode.ForWrite) as Parcel;

// Read properties
double area      = parcel.Area;       // square feet/meters (drawing units)
double perimeter = parcel.Perimeter;

// Set writable properties
parcel.Name    = "Lot 15";
parcel.Number  = 15;
parcel.Address = "123 Main St";
parcel.TaxId   = "R-2026-0015";
parcel.LandUse = "Residential";
parcel.StyleId = parcelStyleId;

Creating Parcels from Objects

// Create parcels from AutoCAD entities (lines, arcs, polylines)
// Entities must form closed boundaries within the site
ObjectIdCollection entityIds = new ObjectIdCollection();
entityIds.Add(polylineId1);
entityIds.Add(polylineId2);

Site site = ts.GetObject(siteId, OpenMode.ForWrite) as Site;
site.CreateParcelsFromObjects(entityIds, parcelStyleId, labelStyleId);

Subdivision

Layout tools create parcels using subdivision algorithms. Civil 3D supports three modes:

• Frontage — subdivides a parent parcel along a frontage line (road alignment), constrained by minimum width and area
• Sliding Angle — sweeps lot lines at a specified angle from the frontage, constrained by minimum area/frontage and side (left or right)
• Free Form — manually defined boundaries within a parent parcel

Note: Subdivision methods are primarily interactive (wizard-driven in the Civil 3D UI). The .NET API supports creation from existing geometry via CreateParcelsFromObjects. For complex subdivision scenarios, use SendStringToExecute to invoke built-in subdivision commands.

Parcel Segments

Parcel boundaries are composed of ParcelSegment objects (lines and curves):

Parcel parcel = ts.GetObject(parcelId, OpenMode.ForRead) as Parcel;

int segmentCount = parcel.Segments.Count;
foreach (ParcelSegment segment in parcel.Segments)
{
    ed.WriteMessage("Segment: Start=({0:F2},{1:F2}), End=({2:F2},{3:F2})\n",
        segment.StartPoint.X, segment.StartPoint.Y,
        segment.EndPoint.X, segment.EndPoint.Y);

    if (segment.IsCurve)
    {
        ed.WriteMessage("  Curve: Radius={0:F2}, ArcLength={1:F2}\n",
            segment.Radius, segment.Length);
    }
    else
    {
        ed.WriteMessage("  Line: Bearing={0}, Length={1:F2}\n",
            segment.Direction, segment.Length);
    }
}

Parcel Topology

Parcels in a site maintain topological relationships. When boundaries are shared, modifying one parcel automatically updates its neighbors.

Adjacency and Parent/Child

Parcel parcel = ts.GetObject(parcelId, OpenMode.ForRead) as Parcel;

// Check if this parcel is an enclosing (parent) parcel
bool isEnclosing = parcel.IsEnclosingParcel;

// Get the site to discover all parcels and their relationships
Site site = ts.GetObject(parcel.SiteId, OpenMode.ForRead) as Site;
ObjectIdCollection allParcelIds = site.GetParcelIds();

// Typically the largest parcel is the "remainder" or parent lot
// Child lots are carved from it via subdivision
// The enclosing parcel updates automatically as child lots are created

Right-of-Way

Right-of-way (ROW) parcels are created when alignments pass through a site. The alignment splits the site into parcels, and the ROW parcel represents the road corridor.

// When an alignment is added to a site, it automatically creates
// ROW parcels by splitting existing parcels along the alignment
// ROW width is controlled by alignment offset parameters

// Check parcel style to identify ROW parcels
Parcel parcel = ts.GetObject(parcelId, OpenMode.ForRead) as Parcel;
ParcelStyle style = ts.GetObject(parcel.StyleId, OpenMode.ForRead) as ParcelStyle;
string styleName = style.Name; // e.g., "Right Of Way" or "ROW"

Parcel Styles

// Create a parcel style
ObjectId styleId = doc.Styles.ParcelStyles.Add("Residential Lot");
ParcelStyle style = ts.GetObject(styleId, OpenMode.ForWrite) as ParcelStyle;

// Display settings - plan view
style.GetDisplayStylePlan(ParcelDisplayStyleType.ParcelSegment).Color =
    Color.FromColorIndex(ColorMethod.ByAci, 3); // green
style.GetDisplayStylePlan(ParcelDisplayStyleType.ParcelSegment).Lineweight =
    LineWeight.LineWeight040;

// Fill display
style.GetDisplayStylePlan(ParcelDisplayStyleType.ParcelAreaFill).Visible = true;
style.GetDisplayStylePlan(ParcelDisplayStyleType.ParcelAreaFill).Color =
    Color.FromRgb(200, 255, 200); // light green fill

// Assign to parcel
parcel.StyleId = styleId;

// Access existing styles
ObjectId existingStyleId = doc.Styles.ParcelStyles["Standard"];

Parcel Labels

Label Style Hierarchy

var parcelLabelStyles = doc.Styles.LabelStyles.ParcelLabelStyles;

// Area labels (placed inside the parcel)
var areaLabelStyles = parcelLabelStyles.AreaLabelStyles;

// Segment labels (placed along boundaries)
var lineLabelStyles = parcelLabelStyles.LineLabelStyles;
var curveLabelStyles = parcelLabelStyles.CurveLabelStyles;

Creating Labels

// Area label (placed at parcel centroid)
Point2d labelLocation = new Point2d(parcel.Centroid.X, parcel.Centroid.Y);
ObjectId areaLabelId = ParcelLabel.Create(
    parcelId, areaLabelStyleId, labelLocation);

// Line segment label
ObjectId lineLabelId = ParcelSegmentLabel.Create(
    parcelId, segmentIndex, lineLabelStyleId);

// Curve segment label
ObjectId curveLabelId = ParcelSegmentLabel.Create(
    parcelId, segmentIndex, curveLabelStyleId);

// Get existing labels
ObjectIdCollection existingLabels = parcel.GetAvailableLabelIds();

// Change label style
Label label = ts.GetObject(areaLabelId, OpenMode.ForWrite) as Label;
label.StyleId = newLabelStyleId;

Common Parcel Label Property Fields

Area labels:

<[Parcel Name(CP)]>
<[Parcel Number]>
<[Parcel Area(Usf|P0|RN|AP|Sn|OF)]>
<[Parcel Perimeter(Uft|P2|RN|AP|Sn|OF)]>
<[Parcel Address(CP)]>
<[Tax ID(CP)]>

Segment labels (line):

<[Segment Bearing(Udir|P0|B4)]>
<[Segment Length(Uft|P2|RN|AP|Sn|OF)]>

Segment labels (curve):

<[Segment Arc Length(Uft|P2|RN|AP|Sn|OF)]>
<[Segment Radius(Uft|P2|RN|AP|Sn|OF)]>
<[Segment Delta Angle(Udeg|P4)]>
<[Segment Chord Length(Uft|P2|RN|AP|Sn|OF)]>
<[Segment Chord Bearing(Udir|P0|B4)]>

Renumbering

// Renumber parcels sequentially
Site site = ts.GetObject(siteId, OpenMode.ForRead) as Site;
ObjectIdCollection parcelIds = site.GetParcelIds();

int lotNumber = 1;
foreach (ObjectId pid in parcelIds)
{
    Parcel p = ts.GetObject(pid, OpenMode.ForWrite) as Parcel;

    // Skip ROW or enclosing parcels
    if (p.IsEnclosingParcel) continue;

    p.Number = lotNumber;
    p.Name = string.Format("Lot {0}", lotNumber);
    lotNumber++;
}

Note: GetParcelIds() does not guarantee any specific ordering. For specific ordering (e.g., clockwise around a cul-de-sac), sort parcels by centroid angle or frontage station before renumbering.

Parcel Analysis

Area and Frontage Checks

double minArea = 7500.0;  // minimum 7,500 sq ft

Site site = ts.GetObject(siteId, OpenMode.ForRead) as Site;
foreach (ObjectId pid in site.GetParcelIds())
{
    Parcel p = ts.GetObject(pid, OpenMode.ForRead) as Parcel;
    if (p.IsEnclosingParcel) continue;

    if (p.Area < minArea)
        ed.WriteMessage("WARNING: {0} area {1:F0} sf < minimum {2:F0}\n",
            p.Name, p.Area, minArea);
}

Summary Statistics

double totalArea = 0, minLot = double.MaxValue, maxLot = double.MinValue;
int lotCount = 0;

foreach (ObjectId pid in parcelIds)
{
    Parcel p = ts.GetObject(pid, OpenMode.ForRead) as Parcel;
    if (p.IsEnclosingParcel) continue;
    totalArea += p.Area;
    minLot = Math.Min(minLot, p.Area);
    maxLot = Math.Max(maxLot, p.Area);
    lotCount++;
}

ed.WriteMessage("Lots: {0}, Min: {1:F0} sf, Max: {2:F0} sf, Avg: {3:F0} sf\n",
    lotCount, minLot, maxLot, totalArea / lotCount);

Enumerating All Parcels

// Enumerate all parcels across all sites
ObjectIdCollection siteIds = doc.GetSiteIds();
foreach (ObjectId siteId in siteIds)
{
    Site site = ts.GetObject(siteId, OpenMode.ForRead) as Site;
    foreach (ObjectId parcelId in site.GetParcelIds())
    {
        Parcel parcel = ts.GetObject(parcelId, OpenMode.ForRead) as Parcel;
        ed.WriteMessage("[{0}] {1}: {2:F0} sq ft\n",
            site.Name, parcel.Name, parcel.Area);
    }
}

Gotchas

• All parcels must belong to a site — there is no "siteless" parcel concept (unlike siteless alignments)
• Adding an alignment to a site automatically splits existing parcels, creating ROW parcels
• Parcel topology is enforced within a site — editing one boundary updates adjacent parcels
• Parcel.Area and Parcel.Perimeter are read-only computed properties based on segment geometry
• ParcelSegment.Direction is in radians measured from north (not east), clockwise positive
• Subdivision methods (frontage, sliding angle) are interactive — the .NET API primarily supports creation from existing geometry via CreateParcelsFromObjects
• GetParcelIds() does not guarantee any specific ordering — sort manually for renumbering
• The enclosing (remainder) parcel updates automatically as child lots are created or deleted
• Parcel Number is an integer property, not a string — use Name for alphanumeric identifiers like "Lot 15A"
• Modifying parcel segments directly is limited — use site topology operations or recreate from objects
• When a site contains both parcels and alignments, deleting an alignment merges the parcels it previously split
• ParcelSegment curve properties (Radius, CenterPoint, IsClockwise) throw if accessed on a line segment — check IsCurve first

Related Skills

• c3d-alignments — alignments within sites and their relationship to parcel topology
• c3d-surfaces — surface-based grading and elevation data for parcel design
• c3d-label-styles — general label style creation and configuration
• c3d-root-objects — CivilDocument access, GetSiteIds(), and transaction patterns