【Geography General】 Maps and GIS: Let’s Get to Know Our World Correctly!
Hello everyone! Starting today, we’re going to dive into one of the major themes of "Geography General": "Maps and GIS." You might be thinking, "Isn't it enough to just look at maps on my smartphone?" But by understanding how maps are made and the technology behind them (GIS), you’ll be able to protect yourself from disasters and identify challenges in your own community. It might feel a bit difficult at first, but don't worry—we’ll go through it slowly using relatable examples!
1. Roles and Types of Maps
There are two main types of maps. The key is to choose the right one for your purpose!
(1) General Maps
These maps provide a comprehensive overview of the Earth's surface. Example: Topographic maps from the Geospatial Information Authority of Japan. Rather than focusing on a specific goal, they display "balanced information" such as roads, buildings, and mountain elevations.
(2) Thematic Maps
These maps are created to focus on a specific theme. Example: Hazard maps (disaster prevention), statistical maps (population density, etc.), and transit route maps. Use these when you have a clear idea of "what you want to know."
Tip: It’s easy to think of it this way: "General maps are like a dictionary, and thematic maps are like specialized textbooks!"
2. Map Projections: The Magic of Flattening a Round Earth
The Earth is a sphere, but maps are flat. If you try to flatten an orange peel, it will inevitably tear or stretch. How we handle this "distortion" is known as map projection.
(1) Mercator Projection
Feature: Angles are represented correctly (Conformal Projection). Advantage: Because it preserves the angle of a straight line between two points (rhumb line), it has been used as a nautical chart for a long time. Caution: The closer you get to high latitudes (near the North or South Poles), the more the area is enlarged compared to reality. Example: On a Mercator projection, Greenland looks about the same size as Australia, but in reality, Australia is much larger!
(2) Mollweide Projection
Feature: Areas are represented correctly (Equal-Area Projection). Advantage: Suitable for distribution maps (population density, forest area, etc.). Caution: The shapes become significantly distorted toward the edges of the map.
Common Mistake: There is no such thing as a "perfect map" that gets everything (angle, area, and distance) right! As long as you are flattening a sphere, something will always be sacrificed.
3. Reading Topographic Maps: Understanding the "Language" of Maps
To read a topographic map, it’s essential to understand the scale (size) and contour lines (elevation).
(1) Calculating Scale
This is the calculation to convert the distance on a map to the actual distance. Formula: Actual distance = Distance on map × Denominator of the scale
Example: If the distance between two points is 4 cm on a 1:25,000 scale map
\( 4 \text{cm} \times 25,000 = 100,000 \text{cm} \)
\( 100,000 \text{cm} = 1,000 \text{m} = 1 \text{km} \)
The answer is 1 km!
(2) Contour Lines
Lines connecting points of the same elevation. ・Narrow spacing: The slope is steep (e.g., cliffs). ・Wide spacing: The slope is gentle.
Fun Fact: On a 1:25,000 scale map, thin lines (index contours) are drawn every 10m, and thick lines (intermediate contours) every 50m. Try to remember the rhythm: "10 for index, 50 for intermediate!"
4. GIS (Geographic Information System) and Modern Maps
This is the most important part of modern geography: GIS!
(1) What is GIS?
GIS (Geographic Information System) is a system used to layer and analyze location-related information on a computer.
(2) The Concept of "Layering"
The biggest feature of GIS is managing information like stacking transparent sheets. ・Layer 1: Road data ・Layer 2: Building data ・Layer 3: Elevation (height) data By stacking these, you can instantly perform analyses like "Which buildings are located in low-lying areas?"
(3) GNSS (Global Navigation Satellite System)
Technology that uses artificial satellites to pinpoint your current location. The "GPS" on your smartphone is one type of GNSS. Because of this, we can obtain accurate map information in real-time.
Point: GIS is an indispensable tool in modern society for things like planning new convenience store locations (where are there many customers?) and evacuation planning during disasters (which roads are prone to flooding?).
Summary
・General maps focus on balance, while thematic maps focus on purpose.
・The Mercator projection is accurate for angles (nautical charts), while the Mollweide projection is accurate for areas (distribution maps).
・To calculate scale, multiply the centimeters by the denominator, then convert to meters or kilometers!
・GIS is about "layering information" and is a powerful tool for solving modern challenges.
Understanding the basics of maps is like putting on a pair of "glasses" that let you see the world objectively. Next time, we’ll think about how to use these maps to solve actual disaster prevention issues and community challenges! Great work today!