How do I create a topographic map in ArcMap?

Creating a topographic map in ArcMap involves processing Digital Elevation Model (DEM) data to generate contour lines and a hillshade effect, then symbolizing these and other geographic features for a clear and comprehensive representation of terrain. This process allows for detailed visualization of elevation, slopes, and landforms.

Understanding Topographic Maps

A topographic map is a detailed, accurate graphic representation of features that appear on the Earth's surface. These features include:

• Elevation: Shown using contour lines and hillshade.
• Hydrography: Rivers, lakes, and other water bodies.
• Infrastructure: Roads, buildings, power lines.
• Vegetation: Forests, open areas.
• Cultural Features: Place names, boundaries.

The core of a digital topographic map in ArcMap relies on a Digital Elevation Model (DEM), which is a raster grid where each cell value represents the elevation at that location.

Essential Data for Topographic Mapping

Before you begin, ensure you have the necessary geographic data:

• Digital Elevation Model (DEM): This is the fundamental input for generating contours and hillshade. You can obtain DEMs from various sources, such as the USGS EarthExplorer for U.S. data or national geospatial agencies worldwide.
• Optional Vector Data: For a more complete map, you might also include vector data like:
  • Roads
  • Rivers and lakes
  • Buildings
  • Administrative boundaries

Step-by-Step Guide to Creating a Topographic Map in ArcMap

Follow these steps to construct your topographic map:

1. Add Your DEM Data

1. Open ArcMap and start a new map document.
2. Click the Add Data button (yellow plus sign) on the Standard toolbar.
3. Navigate to your DEM file (e.g., a .tif or .asc file) and click Add. Your DEM will appear in the Data View and in the Table of Contents.

2. Generate Contour Lines

Contour lines are lines on a map that connect points of equal elevation, providing a visual representation of the terrain's shape and slope.

1. Open ArcToolbox (red toolbox icon on the Standard toolbar).
2. Navigate to Spatial Analyst Tools > Surface > Contour.
3. In the Contour dialog box:
   • Input raster: Select your loaded DEM.
   • Output polyline features: Specify an output location and filename (e.g., ContourLines.shp).
   • Contour interval: This is the vertical distance between adjacent contour lines. A common interval for detailed maps might be 5 or 10 meters/feet, while for broader areas, 20 or 50 might be appropriate.
   • Base contour (optional): The starting elevation for contour generation.
   • Z-factor (optional): Use if your horizontal and vertical units are different (e.g., meters horizontally, feet vertically).
4. Click OK to generate the contour lines.

Practical Insight: Major and Minor Contours

For readability, topographic maps often differentiate between major and minor contour lines. Major contours are typically bolder and labeled with their elevation, usually occurring at every fifth or tenth contour interval (e.g., every 50 meters if the interval is 10 meters).

To achieve this:

• Generate two sets of contour lines: one for major intervals and one for minor intervals, or
• After generating all contours, use a definition query or selection by attributes to select contours that are multiples of your major interval (e.g., CONTOUR % 50 = 0) and apply different symbology.

3. Create a Hillshade Effect

A hillshade raster uses an illumination source to create a 3D-like effect, making the terrain's relief more visually apparent.

1. In ArcToolbox, navigate to Spatial Analyst Tools > Surface > Hillshade.
2. In the Hillshade dialog box:
   • Input raster: Select your DEM.
   • Output raster: Specify an output location and filename (e.g., Hillshade.tif).
   • Azimuth (optional): The sun's relative angle from true north (0-360 degrees). Default is 315 degrees (northwest).
   • Altitude (optional): The sun's angle above the horizon (0-90 degrees). Default is 45 degrees.
   • Z-factor (optional): Use if your horizontal and vertical units are different.
3. Click OK.

To add a realistic visual representation of the terrain's relief, you'll create a hillshade. Navigate to the ArcToolbox, expand Spatial Analyst Tools, then Surface, and select Hillshade. In the Hillshade dialog box, the Input raster will be your DEM. For Azimuth and Altitude, you can generally leave the default values, which are typically suitable for most analyses.

4. Symbolize Your Map Layers

Effective symbology is crucial for a readable and informative topographic map.

1. Hillshade:
   • Right-click the Hillshade layer in the Table of Contents and select Properties.
   • Go to the Display tab and adjust the Transparency (e.g., 40-60%) to allow other layers to show through.
   • Consider changing the color ramp to a grayscale if it isn't already.
2. Contour Lines:
   • Right-click your ContourLines layer and go to Properties > Symbology.
   • For major contours, use a thicker, darker brown line (e.g., 1.5 pt).
   • For minor contours, use a thinner, lighter brown line (e.g., 0.5 pt).
   • You can symbolize categories by the CONTOUR field if you want to apply different colors or thicknesses based on elevation.
3. Other Vector Layers (Optional):
   • Rivers/Lakes: Blue lines/polygons.
   • Roads: Red or black lines, varying thickness by road type.
   • Buildings: Gray or black polygons.
   • Vegetation: Green polygons.

Common Topographic Symbology Guidelines

Feature Type	Recommended Color	Style	Example Use
Contour Lines	Brown	Thin lines, thicker for major	Showing elevation and terrain shape
Hydrography	Blue	Lines for rivers, polygons for lakes	Water bodies and drainage patterns
Roads	Red / Black	Various line styles	Transportation networks
Vegetation	Green	Pattern fill or transparent overlay	Forested areas, open fields
Buildings	Black / Gray	Solid fill polygons	Urban and developed areas
Text/Labels	Black	Clear, legible fonts	Naming features, elevations

5. Label Your Features

Labeling helps identify specific features and elevation values.

1. Contour Labels:
   • Right-click the ContourLines layer and select Label Features.
   • To customize, right-click again and go to Properties > Labels tab.
   • Set the Label Field to CONTOUR.
   • Adjust font size, color, and placement options (e.g., Placement Properties > Placement > Contour Placement) for clarity.
2. Other Labels: Label rivers, roads, and key landmarks as needed.

6. Create a Map Layout

The map layout is where you finalize your map for printing or export.

1. Switch to Layout View (File > Layout View or the button on the bottom-left of the map display).
2. Add essential map elements:
   • Title: Insert > Title.
   • North Arrow: Insert > North Arrow.
   • Scale Bar: Insert > Scale Bar. Choose an appropriate style.
   • Legend: Insert > Legend. Customize which layers are shown.
   • Text/Credits: Insert > Text to add data sources, author, and date.
3. Adjust the map frame and element positions for an aesthetic and informative presentation.

7. Export Your Map

Once your layout is complete, you can export it to various formats.

1. Go to File > Export Map...
2. Choose your desired format (e.g., PDF, JPEG, TIFF).
3. Set resolution (DPI) and output location.
4. Click Export.

By following these steps, you can effectively create detailed and visually appealing topographic maps in ArcMap, leveraging DEM data to convey crucial information about the Earth's surface.