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How do you organize Earth science data into a table or graph and read a trend from it?

Organize, analyze and interpret data using tables and graphs (line, bar, scatter), identify trends and the relationship between variables, and calculate the rate of change and percent (Virginia 2018 Earth Science SOL ES.1).

A SOL-level answer on data and graphs for the Virginia Earth Science EOC: choosing the right graph type, putting the independent variable on the x-axis, reading and describing trends, interpolating and extrapolating, calculating rate of change and percent deviation, and what a gradient on a map means, with worked exam questions.

Generated by Claude Opus 4.813 min answer

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  1. What this topic is asking
  2. Choosing the right graph
  3. Reading a trend
  4. Interpolation and extrapolation
  5. Rate of change and gradient
  6. Percent deviation
  7. Try this

What this topic is asking

Virginia Earth Science SOL standard ES.1 asks you to organize and interpret data. The EOC is heavily data-driven: items hand you a table, a line graph, a bar graph or a map and ask you to read a value, describe the trend, predict a value, or calculate a rate of change or a percent. The ability to read a graph quickly and correctly is one of the most valuable test skills, because it shows up across every reporting category.

Choosing the right graph

By convention the independent variable (what you changed) goes on the x-axis and the dependent variable (what you measured) goes on the y-axis. This matches the variables you identified when you designed the investigation.

Reading a trend

A trend is the overall direction of the data once you ignore small bumps. A line that rises from left to right shows that as the x-variable increases, the y-variable increases too, a direct (positive) relationship. A line that falls shows an inverse (negative) relationship. A flat line shows no relationship. On the EOC, "describe the relationship" wants the direction (as one goes up, the other goes up or down), not a point-by-point retelling.

Interpolation and extrapolation

Rate of change and gradient

A favorite ES.1 calculation is the rate of change, how fast a quantity changes:

rate of change=change in field valuechange in time\text{rate of change} = \frac{\text{change in field value}}{\text{change in time}}

For example, if a temperature rises from 10 degrees C to 22 degrees C over 4 hours, the rate is 22−104=3\frac{22 - 10}{4} = 3 degrees C per hour. The same structure describes a gradient on a map, the change in a field value (elevation, pressure, temperature) over the distance between two points:

gradient=change in field valuedistance\text{gradient} = \frac{\text{change in field value}}{\text{distance}}

A steep slope on a topographic map, or tightly spaced isolines on a weather map, means a large gradient.

Percent deviation

To compare a measured value with an accepted one, use percent deviation (percent error):

percent deviation=∣measured−accepted∣accepted×100%\text{percent deviation} = \frac{|\text{measured} - \text{accepted}|}{\text{accepted}} \times 100\%

A small percent deviation means the measurement is close to the accepted value (accurate).

Try this

Q1. A graph of two variables shows a line that rises steadily from left to right. State the type of relationship. [1]

  • Cue. A direct (positive) relationship: as one variable increases, so does the other.

Q2. A glacier retreats from 500 m to 350 m over 5 years. Calculate the rate of change. [2]

  • Cue. 500−3505=1505=30\frac{500 - 350}{5} = \frac{150}{5} = 30 m per year.

Exam-style practice questions

Practice questions written in the style of VDOE exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

VA Earth Science SOL 2023 (style)1 marksA student records the temperature of a cooling lava sample every minute for ten minutes. Which type of graph is best for showing how temperature changes over time? (A) a pie (circle) graph. (B) a bar graph. (C) a line graph. (D) a map.
Show worked answer →

A 1-point multiple-choice item on choosing a graph type.

The correct answer is C. A line graph is best for showing how one variable (temperature) changes continuously with another (time), so a trend can be read. A pie graph (A) shows parts of a whole, a bar graph (B) compares separate categories, and a map (D) shows spatial data, none of which display a continuous trend over time as clearly.

The test rewards matching the data to the right display: continuous change over time means a line graph.

VA Earth Science SOL 2024 (style)2 marksA river gauge reads a water height of 2 meters at 8:00 a.m. and 5 meters at 11:00 a.m. (a) Calculate the rate of change of the water height. (b) Using the rate, predict the height at 1:00 p.m. if the trend continues, and state what kind of reasoning that prediction uses.
Show worked answer →

A 2-point calculation item using rate of change.

(a) 1 point: rate of change is the change in value divided by the change in time, 5−211−8=3 m3 h=1 m/h\frac{5 - 2}{11 - 8} = \frac{3\ \text{m}}{3\ \text{h}} = 1\ \text{m/h}.
(b) 1 point: from 11:00 a.m. to 1:00 p.m. is 2 hours, so the height rises another 2 m, giving about 7 m; predicting beyond the measured data is extrapolation.

Markers reward the correct rate with units in (a), and the extended value plus the word "extrapolation" (predicting outside the data range) in (b).

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