Map Projections A map projection is used to portray all or part of the round Earth on a flat surface. This cannot be done without some distortion. Every projection has its own set of advantages and disadvantages. There is no "best" projection. Targets: true distance, true areas, true shapes The mapmaker must select the one best suited to the needs, reducing distortion of the most important features. A brief introduction to “projections” will help students understand different perspectives available with world maps. During this intro, it is best to use a globe for reference. Gerardus Mercator (1512-1594).

Mercator projection Robinson projection Used for navigation or maps of equatorial regions. Any straight line on the map is a rhumb line (line of constant direction). Directions along a rhumb line are true between any two points on map, but a rhumb line is usually not the shortest distance between points. Robinson projection Uses tabular coordinates rather than mathematical formulas to make the world "look right." Better balance of size and shape of high-latitude lands than in Mercator, Van der Grinten, or Mollweide. Soviet Union, Canada, and Greenland truer to size, but Greenland compressed. Teacher: Use a globe and paper during this part of lecture to demonstrate projections. Have students take notes about the different types. Source: http://egsc.usgs.gov/isb/pubs/MapProjections/projections.html

Orthographic projection Used for perspective views of the Earth, Moon, and other planets. The Earth appears as it would on a photograph from deep space. Used by USGS in the National Atlas of the United States of America™. Albers Equal Area projection Used by USGS for maps showing the conterminous United States (48 states) or large areas of the United States. Well suited for large countries or other areas that are mainly east-west in extent and that require equal-area representation. Teacher: Use a globe and paper during this part of lecture to demonstrate projections. Have students take notes about the different types. Source: http://egsc.usgs.gov/isb/pubs/MapProjections/projections.html

Resolution low high Image Resolution= pixels/inch Image resolution describes the detail an image holds. The term applies to digital images, film images, and other types of images. Higher resolution means more image detail. The term resolution is often used as a pixel count in digital imaging, even though American, Japanese, and international standards specify that it should not be so used, at least in the digital camera field.[1][2] An image of N pixels high by M pixels wide can have any resolution less than N lines per picture height, or N TV lines. But when the pixel counts are referred to as resolution, the convention is to describe the pixel resolution with the set of two positive integer numbers, where the first number is the number of pixel columns (width) and the second is the number of pixel rows (height), for example as 640 by 480. Another popular convention is to cite resolution as the total number of pixels in the image, typically given as number of megapixels, which can be calculated by multiplying pixel columns by pixel rows and dividing by one million. Other conventions include describing pixels per length unit or pixels per area unit, such as pixels per inch or per square inch. None of these pixel resolutions are true resolutions, but they are widely referred to as such; they serve as upper bounds on image resolution.Below is an illustration of how the same image might appear at different pixel resolutions, if the pixels were poorly rendered as sharp squares (normally, a smooth image reconstruction from pixels would be preferred, but for illustration of pixels, the sharp squares make the point better).