الجيومورفولوجيا - الأودية والخرائط الكنتورية

Contour Maps

• Contour maps are important scientific documents for geographical studies.
• They are fundamental for both human and natural geographical studies.
• In human geography, the topographic map is a general base map with additional data for diagnosing and analyzing geographical problems.
• Contour lines in a topographic map depict surface shapes, elevations, and slopes.
• Surface shapes influence human settlements and their extent, determining settlement patterns and areas of concentration or dispersion.
• Variations in elevation affect climate and consequently, vegetation types.
• Slope affects surface water flow, water availability, and population patterns—also soil erosion and transportation routes.
• Early attempts to represent the Earth's surface on maps were limited by the inability to represent three-dimensional features on a two-dimensional surface.
• Contour lines offered a breakthrough in representing the three-dimensional surface.

Methods of Contour Map Generation

• Method 1: Perspective Drawing: Shows a side view, with an approximative representation of features and slopes but doesn't indicate elevation or slope values. Relies heavily on the artist's skill.
• Method 2: Bench Marks: Measurements of elevations from sea level recorded separately (Robiretes). Don't give a clear sense of relief. It's a precursor for creating more detailed maps.
• Method 3: Contour Lines: Based on precise calculations of elevations from sea level; smooth lines that join all equal elevation points. Depicts the topography in detail.

Contour Lines Characteristics

• Vary in thickness, length, and spacing according to slope variations and shape.
• Thinner, spaced further apart, longer in gentle slopes and absent on flat surfaces; thicker, denser, shorter in steep slopes.
• Often represent hills, plateaus, mountains, valleys, cliffs, ridges, terraces, and ravines.
• Curves to show concave and convex shapes within specific regions.

Data Collection for Contour Maps

• Elevation measurements using surveying instruments such as levels and theodolites.
• Aerial and satellite imagery.
• Using existing datasets from authoritative sources.

Importance and Applications

• Analysis of surface form: Allows for studying the details of landforms and how they are shaped by erosion and weathering.
• Understanding and characterizing terrain: Reveals information on the altitude, slope, and shape of the terrain.
• Planning and construction: Applications in engineering projects like road construction, airport and port sites.
• Study of landform evolution: Used to analyze landform changes over geological time.
• Assessing natural resources: Understanding topography guides decisions on agriculture, water resources, and settlement suitability.
• Military and civilian observation points: The highest points on the terrain are important to assess visibility ranges.

Other Methods for Creating Contour Maps

• Calculation Methods: Based on horizontal and vertical distances between points.
• Graphical Methods: Using transparent triangles (triangle method), parallel lines with a ruler and protractor, and a plotter (for large-scale maps).
• Computer Software: Utilizing Geographic Information Systems (GIS) and AutoCAD programs for accurate and efficient plotting.

Contour Interval

• Represents the vertical distance between consecutive contour lines.
• Determined based on map scale and relief; inversely related to map scale.

Contour Representation

• Closed loops: Depicting hills and plateaus.
• Open contours: Representing valleys, plains, and other lowered areas.
• Intersecting contours: Show features with varying elevations.
• Contour lines that do not branch: Represent uniform levels along them
• Closed loops of contour lines can reveal features such as hills, passes, and depressions.
• Contour lines that converge or diverge indicate changes in elevation.

Additional Contour Map Features

• Water divide: Illustrates the boundaries between drainage basins.
• River meanders: Shows the winding course of rivers.
• River terraces: Displays flattened surfaces along river valleys.
• Waterfalls: Depicts abrupt changes in elevation where rivers drop over cliffs.
• River capture: Demonstrates one river diverting another's flow.
• Gorge/ravine: Narrow valleys, often steep-sided, cut into the landscape.
• Knolls: Small hills, features with isolated peaks or bumps.
• Spurs: Narrow, elongated ridges extending from a main topographic feature.
• Faults: Areas of abrupt change in elevation often resulting from tectonic movement.
• Structural features: Display variations in rock type and orientation.
• Domes: Regions of gently curved terrain with a central high point.
• Cuestas (Steep Slope): A sloping landform resulting from the erosion of a layered rock formation.

Contours and Terrain Analysis

• Analysis of the terrain: Identifying different topographic features like slopes, hills, valleys, and plains.
• Understanding the interplay of surface features: Analyzing the relationship between topographic elements and natural processes.
• Interpretation of topographic features: Deriving the nature of landforms, such as gentle slopes, steep slopes, and abrupt changes.
• Analyzing and representing contour changes: Displaying the evolution of terrain from earlier to later geological stages, or from a younger to older geological age.