Photographs, Sketches and Cross-Sections

Interpreting Cross-Sections and Transects

• Every time you use a map app on your phone to find the flattest route for a bike ride, you are using the exact same skills geographers use to interpret relief and transects.
• A cross-section is a side-profile diagram representing land surface relief along a straight line between two points.
• Relief can be identified on a cross-section using contour lines: close contour lines represent steep slopes, whereas widely spaced lines indicate gentle slopes or flat land.
• Geographers often use vertical exaggeration, making the vertical scale larger than the horizontal scale to ensure subtle changes in relief are visible.
• River profiles have two distinct types: a channel cross-profile shows only the river's width and depth and does not include the surrounding land, whereas a valley cross-profile includes the channel, valley floor, and valley sides.
• Applying the Bradshaw Model to cross-sections reveals a narrow, shallow channel in a steep V-shaped valley in the upper course, changing to a very wide, deep channel with a flat floodplain in the lower course.
• A transect is a line across a landscape along which measurements are taken or observations are made at regular intervals.
• Transects often use systematic sampling to investigate a gradient, such as an urban gradient where building density decreases and green space increases as you move from the Central Business District (CBD) toward the rural-urban fringe.

Calculating Gradients and Sampling Intervals

• The gradient is the steepness of a slope, calculated using the difference in height and distance.
• The Vertical Interval (VI) is the difference in height between the highest and lowest points on a cross-section.
• The Horizontal Equivalent (HE) is the actual ground distance between the two points of the cross-section.

$$Gradient = \frac{\text{Vertical Interval}}{\text{Horizontal Equivalent}}$$

Worked Example: Calculating Gradient

• Step 1: Identify the values. A hill rises $100\,\text{m}$ (VI) over a horizontal distance of $500\,\text{m}$ (HE).

• Step 2: Substitute into the formula. $100 / 500 = 0.2$

• Step 3: Express as a ratio. This is a 1:5 ratio (for every $5\,\text{m}$ traveled horizontally, the land rises $1\,\text{m}$).

Worked Example: Calculating Sampling Intervals for a Transect

• Step 1: Write the formula.

$$\text{Sampling Interval} = \frac{\text{Total Distance}}{\text{Number of Points} - 1}$$

• Step 2: Substitute the values. For a $2\,\text{km}$ ($2000\,\text{m}$) transect with $11$ data points: $2000 / 10$

• Step 3: Calculate the final answer. The interval is $200\,\text{m}$.

Interpreting Ground, Aerial, and Satellite Photographs

• Different photographic perspectives provide different geographical information.
• Ground-level photographs give an eye-level view with high detail of building materials and vegetation, but they do not show spatial patterns behind the immediate foreground.
• A vertical aerial photograph is a $90^\circ$ bird's-eye view with uniform scale, often corrected into an orthophoto for accurate map-making and distance measurement.
• Oblique aerial photographs are taken at an angle ($30^\circ$–$60^\circ$); a high oblique includes the horizon, whereas a low oblique does not include the horizon.
• Satellite imagery is captured from space to show global or regional spatial patterns, such as deforestation or storm systems.
• Interpretation keys include tone/color (bright green for vegetation), texture (rough for woodland), pattern (regular/geometric for human features, irregular for natural features), and shadow (used to determine building height).
• To determine camera direction from a photo, find two prominent features, locate them on an OS map, draw a line from the foreground feature to the background feature, and read the compass direction.

Drawing and Annotating Field Sketches

• A field sketch is a simplified hand-drawn representation used to highlight geographical features from a specific viewpoint (the exact location and angle from which a sketch is made).
• Sketches organize information into perspective layers: the foreground (most detail), middle ground (major features and landforms), and background (horizon and skyline).
• Sketches are qualitative and rely on selective detail, meaning you must deliberately omit irrelevant details like cars or people to focus purely on geographical processes.
• When drawing, use the nine-section method to divide the photo and your drawing frame into a $3 \times 3$ grid to maintain correct proportions, and always draw from the background to the foreground.
• Distinguish between identifying features: a label is a simple identifier (e.g., "Meander"), while an annotation is an explanatory note describing a characteristic or process (e.g., "Meander: formed by lateral erosion").
• Annotation arrows must be drawn with a ruler, touch the exact feature, and never cross each other.

Completing Diagrams, Maps, and Graphs

• When completing graphs, follow strict formatting rules: histograms must have bars of equal width with no gaps, whereas bar charts must have equal gaps between bars.
• Scatter graphs must use a single straight or smooth curved line of best fit; you must not connect the dots in a jagged line.
• When completing pie charts, calculate the size of each segment using the formula: $\text{Segment Degrees} = (\frac{\text{Value}}{\text{Total}}) \times 360^\circ$.
• Triangular graphs are used to plot data with three variables that total $100\%$; you must read or plot values by following the axis in the direction of the slanted grid lines.
• When interpreting data on a graph, use the TEA method: identify the Trend (overall direction), provide Evidence (quote specific figures and units), and spot any anomaly (a data point that does not fit the overall pattern).
• Qualitative data along a transect can be measured using an Environmental Quality Survey (EQS), which scores variables like litter or noise on a numerical scale (e.g., -5 to +5).