Frequently asked questions

What's the difference between true north, magnetic north, and grid north?

True north points to the geographic pole. Magnetic north is where a compass needle points, and it drifts over years. Grid north is the direction defined by a map's printed grid lines, which can differ slightly from true north depending on the projection. A bearing taken with a compass needs a declination correction before it matches the map's grid.

How do I read a contour line without a legend handy?

Look at spacing and closure. Lines packed tightly together mean a steep slope; lines spread apart mean gentler ground. A closed loop with lines pointing outward from the center is usually a hill; a loop with tick marks pointing inward is a depression.

Why do some maps use a different scale than others for the same area?

Scale is chosen for purpose. A regional planning map might use 1:100,000 to show a wide area at low detail, while a trail map of the same region might use 1:24,000 to show individual switchbacks. Neither is more "correct" — they're built for different questions.

What does "1:24,000" actually mean in practice?

One unit of length on the map equals 24,000 of the same unit on the ground. One inch on the map is roughly 2,000 feet on the ground — useful for judging how far a walk between two points on the sheet really is.

How is elevation gain estimated from contour lines alone?

Count how many contour intervals a route crosses between its low and high points, then multiply by the interval printed in the map's margin. It's an estimate, not a survey-grade figure — small dips and rises smaller than the interval won't show up.

Why do coastlines look different on maps at different scales?

Generalization. At a small scale, a cartographer can't print every inlet and rock, so the coastline is simplified into a shorthand version. Zoom into a large-scale chart of the same coast and far more detail reappears.

What is a datum, and why does it matter for older maps?

A datum is the reference surface a map's coordinates are built on. Older maps sometimes used a datum that has since been superseded, so overlaying an old paper map on a modern digital one can show the same coastline shifted by tens of meters.

How do I estimate distance using a graphic scale bar?

Mark the distance between two points on a strip of paper or the edge of a card, then lay that edge against the scale bar printed on the sheet and read off the corresponding ground distance.

Why does a compass bearing sometimes disagree with the map's grid lines?

Because a compass points toward magnetic north, not grid north, and the two aren't the same direction. The difference, called declination, has to be added or subtracted before a bearing taken in the field matches a line drawn on the map.

What's the difference between a topographic map and a road map?

A road map is generalized around transportation — roads, towns, and boundaries. A topographic map is built around the shape of the terrain itself, using contour lines to show elevation, slope, and landform in a way a road map usually leaves out.

Do digital maps still use projections?

Yes. Any flat display of the earth, screen or paper, has to choose a projection. Most web maps default to a Mercator-family projection, which keeps shapes recognizable but stretches area badly near the poles.

Is Contourline affiliated with any mapping agency or survey authority?

No. We're an independent editorial project, not a government agency, a GIS company, or a certified surveying body. Nothing we publish should be treated as an official survey or legal boundary determination.

Do you sell products or take advertising?

We don't run third-party ads or sponsored posts. Waypoint Card is our own companion app and is always clearly labeled as ours whenever it's mentioned.

What is Waypoint Card, and do I need it to read Contourline?

It's a small offline reference app described on our Waypoint Card page. You don't need it to read anything on this site — the journal and the app are separate projects that happen to share a publisher.

How do you fact-check claims about historical maps?

We cross-reference published survey histories and archival cartography wherever possible, and we phrase anything uncertain as an estimate rather than a settled fact. See our content policy for more.