scale & accuracy. the amount of reduction that takes place in going from real-world dimensions...
TRANSCRIPT
SCALE & ACCURACY
•The 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.
SCALE
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.
Verbal 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.
Bar Scales
Large Scale e.g. 1:1000 Small Scale e.g. 1:250000
11000 1
250000
•The 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 1:250000
•Large scale map features are relatively large. Small scale map features are relatively small.
Large Scale vs. Small Scale
•Shows a relatively small portion of the earth’s surface
•Provides detailed information
•Usually maps that are 1:24000 or larger are considered large scale
e.g. 1:24000 - quad scale
e.g. 1:12000 - quarter quad scale
e.g. 1:2400 - tidelands maps
Large Scale
•Shows relatively large areas of the earth
•Provides limited detail
•Generally maps smaller than 1:24000 are considered small scale.
e.g. 1:250,000 - Hudson county
e.g. 1:3,300,000 - State of New Jersey
Small Scale
•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.
Forms of Geographic Phenomena
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ROLLINGGREENS
FARMSTEAD
NEWTON
ANDOVER TWP
Large Scale Small Scale
• All maps are generalizations
• Too much detail for the sake of precision could overwhelm an audience
• Too little attention to detail could result in inaccuracies that misinform or anger an audience
• An accurate map is one that communicates the message clearly, and helps the audience understand the limitations of the data.
ACCURACY
The distance between the actual location of a feature and its mapped location.
Most critical for larger scale maps.
Geometric Accuracy
1:100,000
Roads from USGS TIGER files
1:24000
Roads from NJDOT
•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 feet• GPS +/- 15 feet
Geometric Accuracy (cont.)
•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.
Inaccuracy in source data that cannot be corrected
Use text to explain the factual limits of the map. Especially when ...
Factual Accuracy
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.
Accuracy in Classification
Interpolation is the process of deducing the unknown values that occur between points with definite values. e.g. isolines, addressmatching.
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Accuracy in Interpolation
•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.
Accuracy in Interpolation (cont.)
Accuracy in Interpolation (cont.)
Address 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.
The potential for misinterpretation by map reader
Accuracy in Interpretation
FGDC standards have been published for documenting and testing the spatial accuracy of GIS data.
1941 - 1947 National Mapping Accuracy Standard
1994 FGDC Metadata Standard
1998 FGDC Geospatial Positioning Accuracy Standard
1998 NJDEP Electronic Data Submittal and Interchange Standard
http://fgdc.er.usgs.gov/standards/standards.html
GIS Spatial Data Standards
> 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”
NMAS Horizontal
1:12,000 - 33.3 ft 1:24,000 - 40ft 1:100,000 - 166.7ft
NMAS Verticalnot more than 10% test points in error by more than 1/2 contour interval
Geometric Accuracy of published maps,especially federal topographic and photographic base maps
National Map Accuracy Standards
NMAS focus on the accuracy of paper maps The 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 used
Decisions made on data of known quality are made with greater confidence and are more easily explained and defended.
Why a new standard is needed
NSSDA 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
Geospatial Positioning Accuracy Standards
FGDC National Standard for Spatial Data Accuracy
Suggested horizontal accuracy for large-scale maps by the American Society of Photogrammetry & Remote Sensing (ASPRS):
Scale Feet1:60 0.051:120 0.11:240 0.21:360 0.31:480 0.41:600 0.51:1,200 1.01:2,400 2.01:4,800 4.01:6,000 5.01:9,600 8.01:12,000 10.01:20,000 16.7
FGDC National Standard for Spatial Data Accuracy (cont.)
ArcView Extension (RMSEr2.avx)Implementation of the NSSDA Test
Procedure
Written by N.J.Geological Survey and distributed on www.esri.com website
Example 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.
LAYOUT
. Subject Area
. Title
. Legend
. Scale
. Tables or supporting graphics
. Border or Neatline
. North Arrow
Cartographic Elements
N
EW
S
The Advance of Rabieson Vaccine FieldTest Study Area
4 0 4 8 12 16 20 Miles
March 1993AtlanticCounty
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CountiesRabies Vaccine Field Test Study Area10 mile radius rabies incidents
$ Rabies Incidents
Atlantic
Cumberland
Cape May
Rabies Vaccine Field Test Mapping
The main subject should take up as much space as possible.
Subject Area
•Should clearly convey the map message
•Should be direct and concise
•Subtitles in smaller type can qualify or expand the statement in your title
•Avoid jargon that is unknown to audiences
•Avoid using the word “map” in your title
•Choose a text font that is prominent and readable
Title
•Describes the graphic code delivering the message
•Symbols should look like counterpart on map
•Can warn of uncertainty in data
•Try to create symbols that don’t need a key
•Use a descriptive legend heading whenever possible.
Legend (key)
UNION
ESSEX
BERGEN
New York Bay
3 0 3 6 Miles
N
EW
S
Hudson County Population Density
New York BayCounties
Persons per sq mile2145 - 56055606 - 86558656 - 1076310764 - 2880828809 - 46236
Legend (cont.)
Table of Contents
Extension on the tool bar that allows you to add a customized legend to your layout
•Displays only those features on the layout that appear in the View.
•Provides more flexibility in the way symbols are displayed.
Legend Maker
Atlantic Ocean
Cape May Point
Lower Twp
Num16shd.shp
Cape May LanduseAltered LandsAthletic Fields (Schools)Bare Exposed Rock, Rock Slides, etc.Bay, EstuaryBeachesBrush-Dominant and Bog WetlandsBrushland/ShrublandCedar SwampCoastal WetlandsCommercial and ServicesConiferous ForestConiferous Wooded WetlandsConiferous/Deciduous ForestCranberry BogsCropland and PasturelandDeciduous ForestDeciduous Wooded WetlandsDeciduous/Coniferous ForestExtractive MiningIndustrialInterior WetlandsLake or PondMilitary ReservationsMixed Urban or Built-up LandNon-Tidal MarshesOrchards, Vineyards, Nurseries, Horticultural AreasOther AgricultureOther Urban or Built-up LandRecreational LandReservoirResidentialRiver ChannelSaline MarshesTransitional AreasTransportation/Communication/UtilitiesUndifferentiated Barren LandsVegetated Dune Communities
Municipalities
N
Land UseCape May Point & Vicinity
1000 0 1000 2000 Feet
without Legend Maker
Cape May Point & Vicinity
Land Use
N
Municipalities
Beaches
Brush-Dominant and Bog Wetlands
Brushland/Shrubland
Coniferous/Deciduous Forest
Deciduous Forest
Deciduous/Coniferous Forest
Extractive Mining
Lake or Pond
Non-Tidal Marshes
Other Urban or Built -up Land
Recreational Land
Reservoir
Residential
Saline Marshes
Transportation/Communication/Utilit ies
Vegetated Dune Communit ies
Cape May Landuse
Atlantic Ocean
Cape May Point
Lower Twp
1000 0 1000 2000 Feet
with Legend Maker
•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
Scale
•Points in the direction of true north
•Mandatory if north is anywhere except the top of the page
•Keep small and unobstrusive
North Arrow
•Tables
•Photos
•Floor plans
•Charts
•Statistics
Enhance map info. But don’t overwhelm the map reader.
Tables or Graphics
•Also known as a neat line or map frame
•Defines boundaries and enhances map reading
•Strongly recommended for a formal presentation
N
EW
S
NJCounties
Counties
10 0 10 20 Miles
Border
•Keep all text brief but accurate
•Make sure text is legible
•Use no more than four fonts or text sizes on a map.
•Beware of using decorative type
You must be concerned with both the content and the form of the text.
Typography
•Use plain text for land,italics for water
•Spread the name out along the feature
Grandin Stream
Lingerts Pond
Lingert Ave
State Hwy 173
I- 78
Village Rd
Kilm
er St
Typography (cont.)
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21 TIMBER LA
12 TIMBER LA
ED BURGHOLZER
15 TIMBER LA
Default labeling style
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12 TIMBER LA
ED BURGHOLZER
15 TIMBER LA
21 TIMBER LA
Balloon labeling
•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.
Position of Map Elements
•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.
Position of Map Elements (cont.)
•Minimize 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.
Map Balance
N
EW
S
The Advance of Rabieson Vaccine FieldTest Study Area
4 0 4 8 12 16 20 Miles
March 1993AtlanticCounty
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Counties
Rabies Vaccine Field Test Study Area10 mile radius rabies incidents
$ Rabies Incidents
Atlantic
Cumberland
Cape May
Example of Map Balance
•Streamline map production
•Ensure consistency of design
Templates
N
EW
S
Roadways and RailroadsHightstown
Mai
n
Town BoundaryRoadsMain arteriesRailroads
0.5 0 0.5 Miles
Mercer County
Hightstown
N
EW
S
Hydrologic FeaturesHightstown
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Peddie Lake
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Rocky Brook
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Peddie Lake DamWetlands
Floodprone Areas (USGS)DocumentedUndocumented
Mercer LakesMercer StreamsTown Boundary
%a Dams
0.6 0 0.6 Miles
Mercer County
Hightstown
N
EW
S
ImageryHightstown
Town Boundary
0.6 0 0.6 Miles
Mercer County
Hightstown
The View becomes the layout title.
The View and Legend frames are updated on each consecutive layout
Create a Template from your Layout
1. From the Layout menu, choose Store as Template. The Template Properties dialog appears.
2. Type in a name for your template and select an icon for it. Press OK.
Save a Layout as a Template
1. From the View menu, choose Layout.
2. In the Template Manager dialog, click the template you 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”.
To choose a template for a layout
•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
CONCLUSION