NOTE: This site had a substantial rewrite on 4 May 2013. Overall behavior of the site should be the same as before, but a few details have changed. Please write if you find any bugs. See Contact Info for my email address.
Welcome to MAPfrappe, my interactive site for cartographic “mixtures.” I hope you find it interesting!
— Kelvin Thompson
This page allows you to see an outline of one part of the world overlayed on another part of the world. For example, you can sketch an outline of California in the “Reference Map” below, and then overlay the outline over Italy in the “Comparison Map.” Whatever outline you draw in the top map stays centered in the bottom map.
You need basic knowledge of Google Maps interactions to get the most out of this web page. Visitto learn more about this wonderful service.
Here’s how you can use this page…
1) Click on the top, “Reference” map to draw an outline. Each click makes a new segment of the outline. Click on Close Outline or End Outline to finish one outline and start a new, disconnected outline. You can draw a closed outline (), or an open outline (), or several outlines (). An outline can have as many points as you want. But if you use lots of points, your browser may take a long time to redraw the image.
2) As you draw your outline in the top map, it appears at the center of the bottom map. You can drag and zoom the bottom map to anywhere in the world, and the outline stays in the center of the map. The outline keeps the same real-world size as in the top map, so it may become very large or very tiny in the bottom map.
You can use this page to answer questions like these: How big is Manhattan compared to my home town? How big is Texas compared to France? If I put the Golden Gate Bridge in my neighborhood, what landmarks would it overlap?
Click on this map to mark the points of an outline. Click on Close Outline or End Outline to finish the current outline. Then click on the map again to start an additional outline. You can have several outlines. The outlines in this map appear in the center of the Comparison Map (further below), no matter where you navigate in that map.
Drag this map to move to different parts of the world. Outlines that you drew in the Reference Map (above) appear centered on this map, no matter where you move the map. The outline may change size a bit depending on where you move the map to—see “Shape Distortion” further below.
Do you want to show your friends what you’ve done? Or do you want to come back to it at a later time? Click the button below to generate a permanent URL associated with current outlines and map views. When you use the generated URL to return to this page, outlines and map views will be restored to their current state.
Generated URL: (not requested yet) hidden initially
If you draw the outline at a given latitude in the Reference map, and then view the outline at a different latitude in the Comparison map, the relative orientation of the marker positions will be distorted. This distortion occurs for two different reasons.
First, Google Maps uses afor its maps. By design, this projection distorts distances at different latitudes. Distances are magnified at higher latitudes.
Second, my calculation of comparison marker positions attempts to preserve true distances between markers. These calculations account for the fact that units of longitude have different lengths depending on latitude. The calculations somewhat reverse Mercator distortions of horizontal distances, but not vertical distances.
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Copyright © 2013 by Kelvin Thompson. All Rights Reserved.
Usage note: This page may not be accurate. Don’t depend on it for anything important.