2 SCALEThe amount of reduction that takes place in going from real-world dimensions to the new mapped area on the map plane.Defined as the ratio of map distance to earth distance, with each distance expressed in the same units of measurement.
3 Ratio & Fractional Scales Expressions of ScaleRatio & Fractional Scales11:24,00024000Equates one unit of distance on the map to the corresponding distance on the ground.
4 Verbal Scales One foot equals 24000 feet One inch equals one mile Useful for a quick sense of ground units in familiar units.Unreliable, subject to misinterpretation, invalidated by reduction and enlargement.
5 Bar Scales Most effective Map user can better measure and interpret distances within the map area.Expands or shrinks along with other map distances, so it remains valid over all reductions and enlargements.
6 Large Scale vs. Small Scale 1Large Scale e.g. 1:100010001Small Scale e.g. 1:250000250000The terms “large scale” and “small scale” refer to scale shown as a fraction.1:1000 is a relatively small denominator, yet it is a much bigger fraction (and thus a larger scale) than 1:250000Large scale map features are relatively large. Small scale map features are relatively small.
7 Large Scale Shows a relatively small portion of the earth’s surface e.g. 1: quad scalee.g. 1: quarter quad scalee.g. 1: tidelands mapsShows a relatively small portion of the earth’s surfaceProvides detailed informationUsually maps that are 1:24000 or larger are considered large scale
8 Small Scale Shows relatively large areas of the earth e.g. 1:250,000 - Hudson countye.g. 1:3,300,000 - State of New JerseyShows relatively large areas of the earthProvides limited detailGenerally maps smaller than 1:24000 are considered small scale.
9 Forms of Geographic Phenomena The form is closely related to scale and may change with the level of inquiry.At a small scale a point or line may be sufficient. At a larger scale a polygon may be more appropriate.
11 ACCURACY All maps are generalizations Too much detail for the sake of precision could overwhelm an audienceToo little attention to detail could result in inaccuracies that misinform or anger an audienceAn accurate map is one that communicates the message clearly, and helps the audience understand the limitations of the data.
12 Most critical for larger scale maps. Geometric AccuracyThe distance between the actual location of a feature and its mapped location.Most critical for larger scale maps.
15 Geometric Accuracy (cont.) Small scale data printed on large scale maps can be coarse, oversimplified and misleading.When digitizing from older map sources, note the risk of compounding original error with new error.If digitizing manually make proof plots.Note accuracy of data creation techniques:Addressmatching +/- 200 feetGPS +/- 15 feet
16 Inaccuracy in source data that cannot be corrected Factual AccuracyInaccuracy in source data that cannot be correctedUse text to explain the factual limits of the map. Especially when ...Map features have changed since data was created, and it’s not practical to update it.Too much generalization exists, such as when the data was compiled at a smaller scale than the map.Metadata is a good source of info related to factual accuracy.
17 Accuracy in Classification Classification is a form of generalization, therefore it affects map accuracy.Experiment with different classifications before deciding which one both accurately represents the data and suggests proper interpretation.Be careful of mapping source data whose classification does not exactly fit topic of map.
18 Accuracy in Interpolation Interpolation is the process of deducing the unknown values that occur between points with definite values. e.g. isolines, addressmatching.
19 Accuracy in Interpolation (cont.) Inform audiences that they must take care in interpreting the data.When interpolation is especially sketchy, or if a feature is incomplete, use dashed or dotted lines to relate its approximate nature to the audience.
21 Accuracy in Interpretation The potential for misinterpretation by map readerAddress possible uncertainty in the interpretation of data,symbols and labels.e.g. Pollution concentrations just above a standard might seem much more dangerous than ones just below the standard. Non-detectable levels may be interpreted as zero and seen as far safer than only slightly higher detectable levels.
22 GIS Spatial Data Standards FGDC standards have been published for documenting and testing the spatial accuracy of GIS data.National Mapping Accuracy Standard1994 FGDC Metadata Standard1998 FGDC Geospatial Positioning Accuracy Standard1998 NJDEP Electronic Data Submittal and Interchange Standard
23 National Map Accuracy Standards Geometric Accuracy of published maps,especially federal topographic and photographic base mapsNMAS Horizontal> 1:20,000 not more than 10% test points in error by > 1/30”< 1:20,000 not more than 10% test points in error by > 1/40”1:12, ft 1:24, ft 1:100, ftNMAS Verticalnot more than 10% test points in error by more than 1/2 contour interval
24 Why a new standard is needed NMAS focus on the accuracy of paper mapsThe same processes that make digital cartography so powerful for data analysis and representation complicate accuracy assessment:Errors can be introduced by scale variability, digitizing source materials, processing algorithms, photogrammetry, resolution, and peripheral limitations.Collective error propagation can result in data that are oftentimes inappropriately usedDecisions made on data of known quality are made with greater confidence and are more easily explained and defended.
25 FGDC National Standard for Spatial Data Accuracy Geospatial Positioning Accuracy StandardsNSSDA specifies a positional accuracy test based on comparing the locations of at least 20 points between a test theme and a reference theme of higher precision.Horizontal & Vertical Accuracy is expressed as a function of the distance error (Root-Mean-Squares Error) between the two themes (a check and reference theme) in the x- and y-coordinate directions for horizontal, and z-coordinate direction for vertical.Threshold values are unspecified and left to the discretion of organizations
26 FGDC National Standard for Spatial Data Accuracy (cont.) Suggested horizontal accuracy for large-scale maps by the American Society of Photogrammetry & Remote Sensing (ASPRS): Scale Feet 1: : : : : : :1, :2, :4, :6, :9, :12, :20,
27 ArcView Extension (RMSEr2 ArcView Extension (RMSEr2.avx) Implementation of the NSSDA Test ProcedureWritten by N.J.Geological Survey and distributed on websiteExample on left shows the display of test results for a horizontal accuracy test between a 1:100,000 scale DRG base image and a DLG Hypsography theme with two sets of points checked.
31 Subject AreaThe main subject should take up as much space as possible.
32 Title Should clearly convey the map message Should be direct and conciseSubtitles in smaller type can qualify or expand the statement in your titleAvoid jargon that is unknown to audiencesAvoid using the word “map” in your titleChoose a text font that is prominent and readable
33 Legend (key) Describes the graphic code delivering the message Symbols should look like counterpart on mapCan warn of uncertainty in dataTry to create symbols that don’t need a keyUse a descriptive legend heading whenever possible.
36 Legend MakerExtension on the tool bar that allows you to add a customized legend to your layoutDisplays only those features on the layout that appear in the View.Provides more flexibility in the way symbols are displayed.
39 Scale Can use a combination of bar and verbal or bar and ratio scales. Should not be overly large, easy to read but not prominent.Place in a recessive location
40 North Arrow Points in the direction of true north Mandatory if north is anywhere except the top of the pageKeep small and unobstrusive
41 Tables or Graphics Tables Photos Floor plans Charts Statistics Enhance map info. But don’t overwhelm the map reader.
42 Border Also known as a neat line or map frame Defines boundaries and enhances map readingStrongly recommended for a formal presentation
43 TypographyYou must be concerned with both the content and the form of the text.Keep all text brief but accurateMake sure text is legibleUse no more than four fonts or text sizes on a map.Beware of using decorative type
44 Typography (cont.) Use plain text for land,italics for water Spread the name out along the feature
47 Position of Map Elements Subject Area should be large, and take up the center of the map.Consider placing the most important cartographic elements near the top or left of the map.Less important and supporting map elements can be positioned toward the bottom and right.
48 Position of Map Elements (cont.) Title should be at the top, usually the center but sometimes to the side.North Arrow and Legend should be to the side at the middle or bottom.Scale usually near the bottom.Use a style sheet when a series of related maps are being made, especially by different people.
49 Map BalanceMinimize white space by making the subject area as large as possible.Title, legend, scale and north arrow should be graphically subordinate to the subject area.Balance map elements (imagine hanging a picture).Use the “Size & Position” option under the Graphic Menu to help balance the map.
51 TemplatesStreamline map productionEnsure consistency of design
52 Create a Template from your Layout The View becomes the layout title.The View and Legend frames are updated on each consecutive layout
53 Save a Layout as a Template From the Layout menu, choose Store as Template. The Template Properties dialog appears.Type in a name for your template and select an icon for it. Press OK.
54 To choose a template for a layout 1. From the View menu, choose Layout.2. In the Template Manager dialog, click the templateyou wish to use.3. For more information on the use of templates, follow the instructions for Style Sheets in the “Design Guide for Environmental Maps”.
55 CONCLUSION Follow guidelines as much as possible Don’t be surprised if you have to break the rules once in a while.Have your map reviewed by people less familiar with the subject.Always remember your message