How do I draw a contour line in AutoCAD 2007?

In AutoCAD 2007, you can draw individual contour lines manually using 3D Polylines, or more commonly, generate them automatically from survey data using specialized add-ons like AutoCAD Land Desktop Companion 2007 or AutoCAD Civil 3D 2007, which were the standard tools for this task.

Drawing Contour Lines in AutoCAD 2007

Creating contour lines in AutoCAD 2007 can be approached in two primary ways: manually drawing individual lines based on existing elevation data, or automatically generating multiple contours from survey data using specialized civil engineering extensions. While plain AutoCAD 2007 allows for manual drawing, automated generation from large datasets typically requires more advanced tools.

Manual Creation of Individual Contour Lines

This method is suitable when you have a limited number of elevation points and need to connect specific points of the same elevation, or if you only need to add a single contour line to an existing drawing.

Prepare your data: Ensure you have 3D points (or other elevation indicators) in your drawing.
Start the Polyline command: Type PLINE or 3DPOLY in the command line and press Enter. Using 3DPOLY is recommended for explicit 3D polylines, though PLINE can also create 3D polylines if points have Z-coordinates.
Set the current elevation (optional but useful): For PLINE, you can use the ELEV command to set a default Z-value for new objects if you're drawing on a single plane, or simply input the Z-coordinate directly for each point. For 3DPOLY, you'll input the X,Y,Z coordinates for each vertex.
Draw the line: Click on consecutive points in your drawing that represent the same elevation. Make sure each point's Z-coordinate (elevation) is consistent for that specific contour line.
Complete the line: Press Enter or C (for close) to finish the polyline.
Assign to a layer: Move the new contour line to an appropriate layer (e.g., "C-CONTOUR-100").

Tip: Use Object Snaps (OSNAP), especially NODE (for point objects) or Endpoint/Intersection for existing lines, to ensure accuracy when connecting points.

Automated Generation of Contour Lines from Survey Data

For comprehensive terrain modeling and the creation of numerous contour lines from extensive survey data, the manual approach is impractical. AutoCAD 2007 itself has limited native capabilities for automatically generating contours from raw data without specialized add-ons. The industry standard for this in 2007 was to use AutoCAD Land Desktop Companion (LDC) 2007 or AutoCAD Civil 3D 2007, which are built on top of AutoCAD.

Leveraging Specialized AutoCAD Products (Land Desktop or Civil 3D)

These civil engineering extensions provide robust tools for managing survey data, creating digital terrain models (DTMs), and generating contours efficiently.

General Steps for Contour Generation (using specialized software)

The process typically involves these steps within Land Desktop or Civil 3D:

Import Survey Data: Begin by importing your raw survey data, which usually consists of point files (with X, Y, and Z coordinates), breaklines (lines representing abrupt changes in slope like ridges or ditches), and boundaries (polylines defining the area of interest).
Create a Surface Model: From the imported data, generate a Triangulated Irregular Network (TIN) surface. This surface is a mathematical representation of the terrain, forming a network of non-overlapping triangles.
Access Contour Generation Command: Navigate to the specific command for contour generation (e.g., "Create Contours," "Generate Contours," or "Surface Contours").
Define Parameters: Configure the contour properties, including:
- Major and Minor Intervals: The vertical distance between major and minor contour lines.
- Smoothing Options: To create smoother, more natural-looking contour lines.
- Layer Assignment: Specify layers for major and minor contours.
- Labeling: Options for automatically labeling contours with their elevation.
Select Data and Boundary: The application will prompt you to select all the "levels" in the drawing, which refers to all the relevant elevation data (points, breaklines, and the TIN surface) that define the terrain. Following this, you will typically be prompted to select the boundary that delineates the specific area within which the contours should be drawn.
Generate and Review: Once the parameters are set and selections made, the software will generate the contour lines. Review the contours for accuracy and adjust settings or refine the surface model as needed.

Practical Insight: These specialized tools often allow for dynamic updates, meaning if your survey data changes, the contours can be regenerated automatically.

Third-Party LISP Routines and Add-ons

In situations where Land Desktop or Civil 3D were not available, some users of plain AutoCAD 2007 relied on custom-developed LISP routines or commercial third-party add-ons to provide more automated contour generation capabilities from 3D point data. These tools varied widely in their functionality and user-friendliness.

Best Practices and Tips for Contour Drawing

Regardless of the method used, adhering to certain best practices will ensure accurate and readable contour maps:

Layer Management: Create dedicated layers for major and minor contour lines (e.g., C-CONTOUR-MAJOR, C-CONTOUR-MINOR). This allows for easy visibility control and printing.
Elevation Data Accuracy: The quality of your contour lines is directly dependent on the accuracy of your source elevation data (survey points, existing contours, breaklines).
Contour Interval: Select an appropriate contour interval based on the project scale and the steepness of the terrain. Steeper terrain might require smaller intervals for detailed representation.
Smoothing: Use smoothing options judiciously. While smoothing can make contours look more natural, over-smoothing can distort the actual terrain representation.
Annotation: Label contours with their elevation to enhance readability and understanding of the terrain. Major contours are typically labeled.
Display Settings: Adjust colors, linetypes, and lineweights for different contour types to make them easily distinguishable on the drawing.

Comparison of Methods

Feature	Manual Polyline Creation	Automated Generation (Land Desktop/Civil 3D)
Effort	High and tedious for multiple or complex contours	Low (once data is prepared and surface is built)
Accuracy	Dependent on manual precision and data interpretation	High, based on the accuracy of source data and surface generation algorithm
Data Source	Visual interpretation of points, existing elevations	Survey points (XYZ), breaklines, boundaries, existing surfaces
Best For	Creating single, specific, or supplementary contour lines	Large-scale terrain modeling, generating numerous contours from raw data
Software Needed	Plain AutoCAD 2007	AutoCAD Land Desktop Companion 2007 or AutoCAD Civil 3D 2007

Additional Resources

Introduction to AutoCAD
Understanding Topographic Maps and Contours (conceptual overview by USGS)
Autodesk Civil 3D Overview