Geographic Base Maps; Map Projections;Using MapInfo Help

I. Geographic Base MapsA. DefinitionB. Types

1. TIGER/ Line2. Cadastral3. Planimetric

II. Map ProjectionsA. DefinitionB. Types

III. MapInfo HelpA. Using Index OptionB. Using Search Option

Real world is complex – How do we represent features in GIS?

Features are shown as spatial objects: points, lines, or polygons

0 D 1 D 2 D

Spatial Data Objects:

0 D- (0 dimensional)- 1 coordinate pair or x,y location1 D- (1 dimensional)- 2 coordinate pairs minimum; length only2 D- (2 dimensional)- 3 coordinate pairs minimum; length & width3 D- (3 dimensional)- volume; length, width, & height

Points build lines. Lines build polygons

Geographic Base Map:

The computerized data layer(s) that contain all geographic (spatial) objects that are common to user(s).

The geographic base map is the first layer(s) placed on the GIS display. Other data layers are then placed above and used for analysis in project work.

The needs, uses, or application of the user determinesthe types of map layers and detail required.

THE 3 MOST COMMON BASE MAP FILES

1. TIGER Line

2. CADASTRAL

3. PLANIMETRIC

First major Base map Type: TIGER/ Line files

- Electronic map files (layers) that display various map features

- Developed by U.S. Census Bureau to aid in the census (counting population)

- Topological Integrated Geographically Encoding & Referencing

- Covers the entire United States

USGS Topographical MapTIGER spatial objects captured from USGS 7.5 min. quadrangles

Quads were about 50 sq. mi. (7x7miles)Scale 1:24,000 (1 inch = 2,000 feet)

Features are displayed on the USGS quads (roads, rail, water, contours, etc.)

7.5 min USGS Quad Index for NE Ohio

57,000 Quad Maps in US

Features digitized &spatial objects created in TIGER

7.5 min quad

Example Data Layers (spatial objects) in TIGER 2010

Example Data Layers (spatial objects) in TIGER 2010

Demographic data captured in the Census can be linked to each block & displayed or analyzed.This attribute data is available through the US Census Bureau. dBase files or excel spreadsheets can be created from the attribute data.

Magnified View of selected Census Geography

- 2010

Example of TIGER File –Record Type 1

Until about 1995, the files were available- at a cost

- on tape (not CD)

- had to use a programming language like SAS to translate to the GIS software desired.

TIGER files can be acquired for any county in the US: Free from various websites: http://geodata.gov or http://www.census.gov/geo/www/tiger/tgrshp2010/tgrshp2010.html

Files are provided in ESRI shapefile format. Files can be translated to MapInfo format or opened directly to MapInfo.

Second Major Base map Type: Cadastral- official record describing/ recognizing the legally defined registration of land (property)

- often referred to as the “parcel base map”

- created by County Auditor or Tax Assessor

- used for tax assessment, public services, zoning, etc.

Based on Legal definitions of parcels (property)ie. From a surveyed x,y location, move North 62 degrees East for 157 feet, move South 91 degrees West, move … until reaching the original x,y location thus creating a parcel polygon (area)

Cadastral Base Map Example

Paper Maps are contained in

292 Books in Cuyahoga Co.

About 30 map pages per book 8814 individual paper map pages

Paper maps digitized

Information is historical

Digitized as lines NOT polygons

Cadastral Map: layer examples

Parcel polygons created paid for: by Cleveland Water Dept. Currency: Complete through Nov. 1994

County updates parcel file all year long.

County Auditor’s Office has been updating parcels to the present.

NODIS receives periodic updates to the parcel layer.

Auditor also maintains attribute databases containing informationabout each parcel

Third major Base map Type: Planimetric- Physical features that can be seen on ground are spatially

recorded (mapped)

- Examples of features captured are road edges (curbs), building footprints, railroads, 2 & 10 foot elevation contours, spot (point) elevations, retention walls, driveways, bridges, interstates, recreation areas, and trees.

- Cuyahoga Co. Engineer’s Office – funded the process to create the planimetric layers

- Planimetrics are created from aerial photography

Aerial Photography example

Aerial photography distortions caused by:

- Uneven surface of Earth distorts feature elevations and shapes

- Tilt of airplane can cause photo distortion of features

Distortion from uneven Earth surface:

Distortion due to tilt of airplane:

Orthogonal Rectification:- process to correct the aerial photo distortions

- uses mathematical algorithms to correct

- a very technical, detailed, & complex process

After aerials are rectified:- orthophotos are generated with corrected shape, elevation, and spatial location of the features captured

- There are 1110 orthophotos for Cuyahoga Co.

- orthophotos are spatially located, placed side by side similar to putting a puzzle together

Planimetric data layers are then electronically captured and placed into the correct data layer. Ie. Road edge, building footprint, etc.

Shows the 1,110 individual orthophotos

Flown in 1993, created orthophotos and planimetricsFlown again in 1999- not processed to planimetricsFlown again in 2002- not processed to planimetricsFlown again in 2006, created orthophotos & selected planimetrics (1/2 foot accuracy)Flown again in 2008- not processed to planimetrics

Examples of Planimetric data layers

Planimetric

- NODIS joined all 1110 planimetric files into a seamless layer for the county.

ie. There is ONE data layer for building footprints not 1110 individual building files. This was done for the other planimetric layers.

- positional accuracy of planimetrics layers are high (plus or minus a few inches to a few feet)

What Base Map do I use???

- depends on user application or project

The base map used can be:- 1 or more data layers within one base map type

- or a combination of data layers from more than one base map type

Combination Base Map Example: Planimetric- road edge & Cadastral- parcel

Map Projections:

- The process of converting 3 dimensional features to 2 dimensional objects.

- Over 50 major map projections with many subtypes

- 2 major projection types deal with:

Equal Area

Direction

Map Projection Examples

Equal Area Projectionsattempt to display featureswith lowest amount of area distortion

Direction ProjectionsAttempt to display featuresFor navigational purposes(To get from point A to B)

Direction Projection

Latitude- Longitude

- is NOT a projection

- actual measured angles from the center of the earth

- grids are equal size

- stretches US, Anactica, etc.

U.S. State Plane- Northern Ohio NAD83

- best use is local maps in Northern Ohio

- units are in feet

Any projection type is acceptable to use whenproject work is in a small geographic area.

Large scale maps = small geographic area ie. 1 inch = 50 feet

Small scale maps = large geographic areaie. 1 inch = 50 miles

MapProjections