Making Maps

12.1 Map Functions in GIS

No direct past exam questions have been asked from this section, but it is part of the syllabus and may appear in future exams.

Map functions are the set of tools and operations within GIS software that transform raw spatial data into meaningful, visually effective map displays. They control how geographic features appear on screen or in print.

Core Map Functions

1. Symbolization: Assigning visual symbols to geographic features based on their geometry type:
   • Point symbols: Circles, squares, triangles, or pictographic icons (e.g., hospital cross, school flag)
   • Line symbols: Solid, dashed, dotted lines of varying width and color (e.g., thick red for highways, thin blue for streams)
   • Polygon symbols: Fill colors, hatching patterns, and outlines (e.g., green fill for forests, red hatching for restricted zones)
2. Classification: Grouping continuous data into discrete classes for map display. Common methods include:
   • Equal Interval: Divides the data range into equal-width classes
   • Quantile: Each class has the same number of features
   • Natural Breaks (Jenks): Minimizes variance within classes; maximizes variance between classes
   • Standard Deviation: Classes based on mean and standard deviation of the data
3. Labeling: Automatically or manually placing text labels on map features (road names, building IDs, contour values). GIS uses label placement algorithms to avoid overlaps.
4. Scale Management: Controlling which features are displayed at different zoom levels. For example, at a city scale show only major roads; at a neighborhood scale show all roads and individual buildings.
5. Annotation: Adding explanatory text, callout boxes, or graphic elements that are not linked to spatial features but enhance the map's readability.
6. Map Generalization: Simplifying features for display at smaller scales — eliminating detail, smoothing lines, aggregating small polygons, and displacing overlapping features.

12.2 Map Design and Visual Variables

1. Map Design, Layout, and Visual Hierarchy

• Map Design: The art and science of cartography. It is the process of selecting, symbolizing, and arranging geographic data to communicate a specific message clearly to the user.
• Map Layout: The physical arrangement of the map body and its supporting marginal elements (like the legend, scale, and title) on a digital or printed page.
• Visual Hierarchy: The graphic organization of the map. It is the technique of using contrast, color, and size to guide the reader's eye to the most important information first (the main theme), pushing background information (like a base map) to the visual background.

2. Visual Variables in Map Designing

Visual variables are the graphic building blocks used to create map symbols. To secure full marks, list the core variables defined by cartographer Jacques Bertin:

1. Size: Changing the physical dimension of a symbol (e.g., small, medium, large dots).
2. Shape: Using different geometric forms (e.g., a square for a building, a cross for a hospital).
3. Color Hue: The actual color itself (e.g., red, blue, green).
4. Color Value (Lightness): How light or dark a color is (e.g., light pink vs. dark maroon).
5. Texture: The density or pattern of marks within a polygon (e.g., solid fill vs. cross-hatched lines).
6. Orientation: The direction a symbol is rotated.

3. Using Colors and Sizes to Convey Information

• Using Size (For Quantitative Data): Size is perfectly suited for showing amounts or magnitudes.
  • Example: In a map of Nepal's hydropower plants, you use "Proportional Symbols" where a small circle represents a 10 MW plant, and a massive circle represents a 450 MW plant. The user instantly understands capacity without reading a single number.
• Using Color Hue (For Qualitative Data): Different colors represent entirely different categories of things.
  • Example: A Land Use map where Blue = Water, Green = Forest, and Red = Urban area.
• Using Color Value (For Quantitative Data): Light-to-dark shading represents low-to-high concentrations.
  • Example: A population density map where light yellow means sparse population and dark brown means dense population.

12.3 Map Elements and Map Layout

This section is almost guaranteed to appear. You must know the list of elements and be able to sketch a standard layout.

1. What is a Map Layout and Marginal Information?

A map layout is the final page assembly of the map. Marginal Information refers to all the explanatory elements placed around the edges (margins) of the main map body that help the user understand the data.

• GIS Export Formats: Maps are typically exported as PDF (for high-quality printing), JPEG or PNG (for web and reports), or TIFF (for high-resolution archiving).

2. The Essential Map Elements (The Standard Layout)

A professional GIS map must contain these elements to be legally and scientifically valid:

1. Map Body: The actual spatial data and geographic representation.
2. Title: A clear, concise statement of what the map shows, where, and when (e.g., "Landslide Susceptibility Map of Sindhupalchok, 2024").
3. Legend: The "key" that explains what every symbol, line, and color on the map represents.
4. Scale: Shows the relationship between map distance and real-world distance. Always include both a Scale Bar (visual) and a Scale Text/Ratio (e.g., 1:50,000).
5. North Arrow: Indicates geographic orientation.
6. Inset Map (Locator Map): A small map showing the location of the main study area within a larger, familiar context (e.g., a tiny map of Nepal with a red box showing where Sindhupalchok is).
7. Coordinate System / Projection Info: Tells other engineers exactly what spatial reference frame was used (e.g., WGS 1984, UTM Zone 45N).
8. Author, Date, and Data Sources: Provides accountability and tracks the age of the data.

3. Preparing a Standard Layout (The Sketch)

For questions asking you to "Prepare a layout," draw a large rectangle representing an A4 piece of paper on your exam sheet.

• Draw a neatline (border) just inside the page.
• Dedicate the top 10% to a bold, centered TITLE.
• Dedicate the large, main center area to the MAP BODY (draw a rough shape of a district).
• On the right side or bottom, draw a dedicated box containing the LEGEND.
• In the bottom right corner, draw a small NORTH ARROW and a SCALE BAR.
• In the bottom left corner, draw a small box for the INSET MAP, and below it, write text lines for Author, Date, and Projection.

4. Thematic Maps and Choropleth Maps

• Thematic Map Design Considerations: Designing a thematic map requires knowing your audience. If designing for the general public, you simplify the legend and use intuitive colors. If designing for civil engineers, you include rigorous coordinate system data, highly detailed legends, and strict contour intervals.
• Where and Why do we design Choropleth Maps?
  • What it is: A specific type of thematic map where pre-defined administrative areas (like wards, districts, or provinces) are shaded with different color values representing a statistical variable.
  • Why use it: It is the absolute best way to visualize rates, percentages, or densities aggregated across political boundaries.
  • Where it is used: Mapping the poverty rate per district, population density per ward, or literacy rate per province.

12.4 Choosing a Map Type

1. Types of Maps

Maps are broadly classified into three main categories based on their function:

• General Reference Maps: Designed to show a variety of general geographic features together without emphasizing any single one. Example: A standard Topographic map showing contours, rivers, roads, and settlements equally.
• Thematic Maps: Designed to focus heavily on one specific theme or topic, pushing general reference features to the background. Examples: Soil classification maps, earthquake hazard maps, or choropleth density maps.
• Navigational Maps (Charts): Specifically designed to help users navigate from one place to another. Examples: Aeronautical charts for pilots, nautical bathymetry charts for ships, or road network maps for drivers.

2. Meaning of a Thematic Map

A thematic map is a map specifically designed to show a particular theme connected with a specific geographic area. Unlike general reference maps that show natural and man-made features simply to establish location, thematic maps portray physical, social, political, cultural, economic, or sociological properties (e.g., mapping exactly where high-strength clay soil is located for construction planning).

12.5 & 12.6 Exporting and Printing a Map

No direct past exam questions have been asked from this section, but it is part of the syllabus and may appear in future exams.

The final step in any GIS mapping workflow is exporting the map layout to a file format or printing it as a physical document.

Exporting Map Formats

Printing Considerations

• DPI (Dots Per Inch): For screen display, 96 DPI is standard. For professional printing, use 300 DPI or higher to ensure crisp lines and readable text.
• Color Mode: Screens use RGB (Red, Green, Blue). Commercial printers use CMYK (Cyan, Magenta, Yellow, Black). Colors may shift when converting between modes.
• Paper Size: Standard sizes include A4, A3, A2, A1, and A0. Large-format maps (e.g., engineering drawings) typically use A1 or A0 plotters.
• Scale Consistency: When printing, ensure the output scale matches the intended scale. A 1:25,000 map printed on the wrong paper size will have an incorrect scale bar.
• Margins and Bleed: Allow adequate margins for binding. Professional prints may need "bleed" (extending the design past the trim edge) for borderless output.

End of Chapter 12 – Making Maps