scale & accuracy. the amount of reduction that takes place in going from real-world dimensions...

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

%a

%a

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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