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AGR-CSI53-02 · Lesson 7 · 13 clock hours · lab

Finished Scale Diagrams Using CAD-Lite or Drawing Software

Objective. Students will convert their Lesson 6 rough sketch into a finished scale diagram using digital drawing software, producing a print-ready plan view accurate to the original measurements that could be submitted as a court exhibit.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed professional in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

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Why a Finished Scale Diagram Matters

A rough sketch is your field record — fast, accurate, and disposable. A finished scale diagram is a legal document. Attorneys, judges, and juries rely on it to understand spatial relationships at a crime scene without ever visiting the location. Because it may become a court exhibit, every line, dimension, label, and symbol must be precise, consistent, and traceable back to the measurements you recorded in the field. Errors in a finished diagram can impeach your testimony, confuse the finder of fact, or provide grounds for an appeal. Accuracy is not optional; it is the professional standard.

From Rough Sketch to Digital Drawing

Your Lesson 6 rough sketch contains all the raw data: room dimensions, evidence item positions recorded by two-point measurement or triangulation, fixed reference points, and a north indicator. The finished diagram translates that handwritten data into a clean, to-scale, print-ready plan view. A plan view is a top-down, two-dimensional representation — walls, doors, windows, and evidence items appear as if you are looking straight down from above. No perspective, no shadows, no artistic interpretation.

Digital drawing software speeds up this conversion and produces uniform line weights, precise annotations, and professional output. Common free or low-cost options include RoomSketcher, SketchUp Free, and various CAD-lite applications. Agency-standard software may be required on the job; the workflow principles transfer regardless of the specific tool.

Setting Up the Drawing Environment

Before you place a single wall, configure the software correctly.

Units and scale. Set the drawing units to feet and decimal inches (or metric if your jurisdiction uses metric). Confirm that the software's snap-to-grid or snap-to-object features are active so lines meet cleanly at corners. Choose a scale that fits the finished diagram on the paper size you will use (commonly 8.5 × 11 in. or 11 × 17 in.). A scale of 1 inch = 4 feet or 1 inch = 8 feet is typical for a single room; use a smaller scale (e.g., 1 inch = 10 feet) for larger spaces.

Template or blank canvas. If your software provides a blank floor-plan template, start there. If not, begin with a blank canvas and set the page boundary to match your paper size before drawing.

Building the Diagram Step by Step

Step 1 — Exterior walls. Use the polygon or room tool to draw the outer boundary of the space. Enter each dimension from your rough sketch as you draw each wall segment. Do not estimate; type the value. After closing the polygon, verify that the on-screen dimension labels match your rough-sketch measurements exactly before continuing.

Step 2 — Interior features. Add interior walls, doorways (shown as a quarter-circle swing arc in plan view), and windows (commonly shown as a triple-line symbol in the wall). Again, enter dimensions from your sketch.

Step 3 — Evidence items. Place each evidence item using the same coordinate system you used in the field. If you used two-point measurement from two fixed reference corners, re-create those reference points on the diagram and place the item at the recorded distances. Label each item with its evidence number and a brief description consistent with your written notes.

Step 4 — Annotations and symbols. Add dimension lines and callouts for key measurements. Insert a north arrow aligned to the orientation you recorded in the field. Add a scale bar — a drawn line labeled with its real-world length (e.g., a 2-inch line labeled "8 ft"). Do not rely on printed scale alone; a scale bar remains accurate even if the document is photocopied at a different size.

Step 5 — Legend and title block. Every forensic diagram needs a title block containing: case number, incident address, date of incident, date the diagram was prepared, your name and agency, and a diagram number. The legend explains every symbol used. Both are typically placed in a corner of the drawing, outside the floor plan itself.

The Self-Audit: Your Last Line of Defense

Before printing a final copy, complete the self-audit comparison form provided by your instructor. Lay your printed diagram beside your Lesson 6 rough sketch and check every measurement, every evidence item location, every label, and every symbol. Discrepancies must be corrected in the software and a new print produced. Never hand-correct a printed diagram — corrections must be made in the source file.

The instructor will apply an 8-item accuracy checklist: all room dimensions must be within ±0.05 ft of your rough-sketch values; all five evidence items must be within ±0.1 ft of their rough-sketch locations; the north arrow and scale bar must be present. All eight items must pass.

Safety and Professional Conduct in the Lab

This is a computer lab activity, but professional standards still apply. Save your work frequently — a crashed application can cost you an hour of precise data entry. Never alter the measurement values from your rough sketch to make the diagram "look right." If your diagram looks distorted, the room may genuinely be non-rectangular, or a measurement error occurred in the field; consult your instructor. Falsifying or adjusting measurements is a form of evidence tampering and is a serious professional and legal violation. Treat your digital file with the same chain-of-custody discipline you would apply to physical evidence: do not share it with other students or open others' files.

Key terms8

Plan viewA two-dimensional, top-down representation of a space showing walls, features, and evidence items as seen directly from above, without perspective.
Scale barA drawn line on a diagram labeled with the real-world distance it represents, allowing correct measurement even if the document is reproduced at a different size.
Title blockA standardized information panel on a forensic diagram that records case number, location, dates, preparer's name, and other identifying data required for evidentiary use.
LegendA key on a diagram that defines every symbol, abbreviation, and line type used in the drawing.
Two-point measurementA field technique that locates an evidence item by recording its distance from two fixed reference points, allowing exact re-creation of the item's position on the finished diagram.
North arrowA symbol on a diagram indicating which direction is north, providing spatial orientation consistent with maps and aerial imagery of the scene.
Dimension annotationA labeled line or callout on a diagram that states the measured length of a wall, distance between features, or other spatial value.
Snap-to-gridA software setting that forces line endpoints and object corners to align to a regular grid, preventing small positional errors that accumulate across a complex drawing.

Worked examples4

1. Your rough sketch shows a wall measured at 12.75 ft. On the finished diagram the software auto-labels the wall as 12.70 ft. Is this within the ±0.05 ft tolerance, and what should you do?
  1. Calculate the difference: 12.75 ft − 12.70 ft = 0.05 ft.
  2. Compare to the tolerance: 0.05 ft is exactly equal to the ±0.05 ft limit.
  3. A difference of exactly 0.05 ft is at the boundary of the allowed tolerance — it does not exceed it, so it technically passes; however, best practice is to correct it.
  4. Re-enter the wall length as exactly 12.75 ft in the software dimension field and confirm the label updates to 12.75 ft before moving on.
Answer: The difference of 0.05 ft is at the exact tolerance boundary. Re-enter the precise value (12.75 ft) to eliminate any doubt and ensure the diagram faithfully represents the field measurement.
2. You are choosing a print scale for a room that measures 18.5 ft × 22.0 ft. Your paper is 8.5 × 11 in. with a 0.5 in. margin on each side, leaving a usable area of 7.5 × 10.0 in. What is the minimum scale (largest denominator in '1 in. = X ft') that fits the room on the page with room for a title block at the bottom (reserve 1.5 in.)?
  1. Usable drawing height after title block: 10.0 in. − 1.5 in. = 8.5 in.
  2. Usable drawing width: 7.5 in.
  3. Required scale for the 22.0 ft dimension to fit in 8.5 in.: 22.0 ÷ 8.5 = 2.59 ft/in. — so the scale must be at least 1 in. = 2.59 ft.
  4. Required scale for the 18.5 ft dimension to fit in 7.5 in.: 18.5 ÷ 7.5 = 2.47 ft/in.
  5. The binding constraint is the larger result: 2.59 ft/in.
  6. Round up to the next standard scale: 1 in. = 3 ft (meaning 3 ft per inch), which gives drawn dimensions of 22.0 ÷ 3 = 7.33 in. and 18.5 ÷ 3 = 6.17 in., both fitting within 8.5 in. and 7.5 in. respectively.
Answer: A scale of 1 in. = 3 ft fits both room dimensions within the available drawing area while leaving space for the title block.
3. Evidence item E-3 was located in the field by two-point measurement: 5.40 ft from corner A and 8.20 ft from corner B. On your finished diagram, the software reports the placed item is 5.40 ft from corner A but 8.32 ft from corner B. Does E-3 pass the ±0.1 ft tolerance for evidence item placement?
  1. Check distance from corner A: |5.40 − 5.40| = 0.00 ft — within tolerance.
  2. Check distance from corner B: |8.32 − 8.20| = 0.12 ft.
  3. Compare 0.12 ft to the ±0.1 ft tolerance: 0.12 ft exceeds 0.1 ft.
  4. E-3 fails the tolerance for corner B. Reposition the item in the software until both distances match the rough-sketch values within ±0.1 ft, then verify again.
Answer: E-3 does not pass. The corner B distance is off by 0.12 ft, which exceeds the ±0.1 ft tolerance. The item must be repositioned and both distances re-checked before submission.
4. Your finished diagram uses a scale of 1 in. = 4 ft. You want to draw a scale bar that represents 8 ft. How long should the drawn scale bar line be, and what label should appear on it?
  1. At 1 in. = 4 ft, one inch of drawn length represents 4 real feet.
  2. To represent 8 ft: 8 ft ÷ 4 ft/in. = 2 in.
  3. Draw a line exactly 2 inches long on the diagram.
  4. Label it '8 ft' (or '8 feet') directly below or beside the line.
Answer: Draw a 2-inch line and label it '8 ft'. This gives readers a reference that remains accurate even if the page is photocopied at a different percentage.

The math in this lesson1

Learners compare drawn and measured wall lengths against a ±0.05 ft tolerance.
N-Q.3
Brush up in the math halls at newSchoolWorks.com:
In class: Instructor demonstrates the software interface (polygon room tool, dimension annotation, legend insertion, north-arrow placement, scale bar) using a screen-share walkthrough with students following along on lab computers. · Students input their own Lesson 6 measurements to construct a finished diagram, checking that on-screen dimensions match rough-sketch values at every step before moving to the next room feature. · Students print their diagrams, place them alongside their Lesson 6 rough sketches, and complete a self-audit form verifying that every measurement, item location, and label matches — discrepancies are corrected before submission.
Materials: Lab computers with free or low-cost 2-D drawing software (e.g., RoomSketcher, SketchUp Free, or agency-standard CAD-lite); printed rough sketches from Lesson 6; self-audit comparison form; printer; scale rulers for verification.
Check: Finished diagram compared by instructor against Lesson 6 rough sketch on an 8-item accuracy checklist — all room dimensions within ±0.05 ft of rough sketch, all five evidence items within ±0.1 ft of rough-sketch location, north arrow and scale bar present; all 8 items must pass.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Scene Documentation
1. Which element on a finished scale diagram allows a reader to determine distances correctly even if the document is photocopied at a reduced size?
Scene Documentation
2. A finished crime scene diagram differs from a rough field sketch primarily because the finished diagram:
Scene Documentation
3. During your self-audit you find that a wall labeled 14.30 ft on the finished diagram was recorded as 14.20 ft on your rough sketch. The checklist tolerance is ±0.05 ft. What is the correct action?
Scene Documentation
4. In a plan-view crime scene diagram, a doorway is conventionally represented by:
Scene Documentation
5. Which of the following minimum pieces of information must appear in the title block of a finished forensic scale diagram?
Legal and Ethical Standards
6. A crime scene diagram must be submitted as a court exhibit, but the investigator changed several rough-sketch measurements on the finished diagram to make the room appear more symmetrical. This action is best described as:
Scene Documentation
7. You are placing evidence item E-5 on a finished diagram using two-point measurement. Your rough sketch records 6.80 ft from corner C and 9.50 ft from corner D. After placing the item, the software reports 6.78 ft from corner C and 9.59 ft from corner D. Which measurement fails the ±0.1 ft tolerance?
Scene Documentation
8. When configuring drawing software before beginning a finished scale diagram, the first setting to establish is:
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