ScaleRepresenting Scale on MapsMap ScaleMap scale is a ratioPoint of confusionGeneral Classification of Map ScaleMap Scale and Map ProjectionsFor ExampleScaling UpMaps and GIS - Scaling UpSlide 11Slide 12Maps and GIS - Scaling DownSlide 14Vertical ScaleVertical Scale: Contour LinesSlide 17Scale Question 1Scale Question 2Scale Question 3Scale Question 4Scale Question 5Scale Question 6Scale Questions 7 - 9Slide 25Slide 26Slide 27Choosing a scaleExamplesUsing scale in practiceScale & Accuracy ExampleSlide 32Slide 33Slide 34Slide 35Slide 36ScaleScaleDefinition:The scale of a map is the ratio between distances on the map and the corresponding distances in the real world.Representing Scale on MapsRepresenting Scale on MapsMap ScaleMap Scale•Scale representation on the map:–Representative fraction (RF): “1:100,000”, “1 to 100,000”, or “1/100,000”–Verbal: 1 inch is equal to 50 miles–Graphic: Scale bar10 milesMap scale is a ratioMap scale is a ratio•It is unit-independent•1/1000 > 1/100,000 –(1/100 is greater than 1/100,000)•Thus 1:1000 is a large scale map, showing a smaller region but magnified•1/100,000 is a small scale map, showing a larger regionPoint of confusionPoint of confusion•Scale in most other contexts, even in geography, is not used as a ratio•e.g., data, area, processes, government, & economies•For example: Large scale data (e.g., global temperature distribution), affects large scale processes (e.g., ocean circulation patterns), but this data is shown on small scale maps•Often we circumvent confusion by using terms like “regional scale” or “hill slope scale”, but confusion can still occur if we ask “which is larger?”•Take home message: if/when I ask about “map scale” on an exam I mean the ratio (i.e., small scale = large area), otherwise scale means what you think it should•Notions of small and large are reversed from our conventional thinking when we talk about map scale  large scale refers to looking at a small area in detail•Here are some scale guidelines:–Large scale map  1:400 to 1:50,000–Intermediate scale map  1:50,000 to 1:250,000–Small scale map  1:250,000 and beyondGeneral Classification of Map ScaleGeneral Classification of Map Scale•The representative fraction of a map does not tell us the scale everywhere on the map•Transformations due to projecting maps introduce distortion–The representative fraction (and the scale bar) is only accurate along standard lines or pointsMap Scale and Map ProjectionsMap Scale and Map ProjectionsFor ExampleFor ExampleScaling UpScaling Up•Data created for local areas can be used for larger (regional or national) areas–Note: now we are talking about scale in common terms (not map scale), so “up” implies larger areasMaps and GIS - Scaling UpMaps and GIS - Scaling Up•The river network shown here on a national scale was produced at a much finer scale, and it contains a great deal of detail that cannot be seen at this map scaleMaps and GIS - Scaling UpMaps and GIS - Scaling UpAll the detail that is encoded in this river network data is really only visible and useful when operating at more local scales.This level of detail is not necessary or useful at the national scale. Vector data such as this river may need to be smoothed for scaling up.WhitepineLodgepolepinericewheatScale Effect on MappingWhitepineLodgepolepinericewheatWhat should we call these cells?Scaling upMaps and GIS - Scaling UpMaps and GIS - Scaling UpRaster data may need to be generalized. An aggregation algorithm must be chosen. (aggregating)Maps and GIS - Scaling DownMaps and GIS - Scaling Down•Small scale data contains more detail than large scale data•Using large scale data for analysis at a smaller scale can cause problemsMaps and GIS - Scaling DownMaps and GIS - Scaling DownHere we can see a national scale coastline (shown in red) superimposed over local scale data, we can clearly see the generalization and lack of detailVertical ScaleVertical Scale•As with horizontal scales, vertical scale is related to the level of detail of the information conveyed by the map•Contour lines are often used to define the vertical scale •Contour intervals are usually provided as “X feet” or “X meters” meaning a contour line will be placed on the map marking the X vertical change–For example: “Contour interval 80 feet”•Contour lines are also frequently used in meteorology (e.g., temperature and air pressure)Vertical Scale: Contour LinesVertical Scale: Contour LinesWhat is the contour interval for this example?Vertical Scale: Contour LinesVertical Scale: Contour LinesScale Question 1Scale Question 1•Which map has a larger map scale and which map covers a larger geographic area?–1:1,000,000 or 1:12,000Scale Question 2Scale Question 2•On a map with a scale of 1:100,000 how much distance is represented by 2 cm?Scale Question 3Scale Question 3•USGS topographic maps (commonly called quadrangles) have a scale of 1:24000•Using such a map to plan a hike, you determine that the trail is 11 3/8 inches long•How far will you be hiking?Scale Question 4Scale Question 4•Given the representative fraction 1:1,000,000, what is the verbal scale (i.e., the word statement that conveys scale) in cm-to-km?Scale Question 5Scale Question 5•Given the representative fraction 1:62,500, what is the verbal scale (i.e., the word statement that conveys scale) in inches-to-miles?Scale Question 6Scale Question 6•How many pixels (a.k.a. raster or GRID cells) from a Landsat image are required to cover a square mile?–Landsat pixels have 30-meter spatial resolution–1 mile ~ 1.61 kmScale Questions 7 - 9Scale Questions 7 - 9Approximately how much elevation did we gain on this hike? Approximately how far did we hike in straight-line distance?Approximately how far did we hike in actual distance?Scale Questions 7 - 9Scale Questions 7 - 9•Approximately how much elevation did we gain on this hike? •Approximately how far did we hike in straight-line distance?•Approximately how far did we hike in actual distance?Panoramic photo taken at sunrise from ~1000 ft below the below the summitChoosing a scaleChoosing a scale•The scale of your data should be chosen according to: 1. Your data needs2. The intended use of the existing dataExamplesExamples•Your data options are:–Landsat TM data (30 meter resolution)–SPOT satellite imagery (5 meter resolution)–Ikonos satellite data (1