Data formats

3/22/2015
Data formats (and projections)
… the fuel for GIS
Early days (pre-UNBC) 1990 or 1994 ?
Not much data, no standard formats
Many different GIS software packages
BC TRIM
Data captured: 1980-89
Prepared : 1990- 95 (complete 1995)
The Spatial Archive and Interchange Format (SAIF, pronounced safe)
was defined in the early 1990s as a self-describing, extensible format
designed to support interoperability and storage of geospatial data –
also known as known as MOEP binary, and became a precursor to GML
.saf = zipped file version
Not a standard format (except in BC government)
UNBC purchased ‘trim2dxf.exe’ – convert TRIM SAIF to (AutoCad) DXF
Import DXF into Arc/Info
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Other GIS / mapping formats
Many more can be converted with FME (Feature Manipulation Engine - 1996) from
(Vancouver based 1993)
http://www.safe.com
We applied for the domain in 1993, when the Internet was just starting to take
off. It is "safe" to say that we would not be able to get this name today!
ArcGIS Data Interoperability FME workbench extension
(ESRI) GIS file formats
Shapefiles (ESRI) Arcview (1994 -> )
.shp
.shx
.dbf
Spatial data
Index link file
Attribute data
e.g. rivers.shp
e.g. rivers.shx
e.g. rivers.dbf
Also:
.prj Projection file (when projected and defined)
.sbn and .sbx .. optimise spatial queries
http://en.wikipedia.org/wiki/Shapefile
Note: you need all these files for one GIS layer
Shapefiles became standard with ArcGIS (2000)
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Coverage (ESRI) - Arc/Info (1981)
Layer name folder
Info folder
e.g. roads (spatial) : 6-20 files
(attributes): many files
Proprietary format – data is not usable by other programs
Coverage (ESRI) - Arc/Info (1981)
Layer name folder
e.g. fc93j10 (spatial)
: 6-20 files (line/polygon)
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Info contents (feature attribute tables)
ESRI GIS vector formats
Export / Interchange format: .e00
(increments to .e01 then .e02)
All arc (spatial) and info files for one theme – zipped into one file
Export coverage -> e00
Import e00 -> coverage
( … and convert or export to shapefile)
Some operations in arcmap require one of Shapefile v Coverage
- It can’t be done with the other
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Raster formats: ASCII GRID
ASCII formats are easy to import / transfer, but bulky in size
Binary GRIDs
Binary format
A binary ESRI grid is stored in several files contained in at least two
directories: the name directory and an info directory
http://support.esri.com/index.cfm?fa=knowledgebase.techarticles.artic
leShow&d=30616
Default format for raster in ESRI: some operations require GRD (?)
Not easy to transfer ! (export to a very bulky e00)
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Files created when you generate a DEM, default (.grd = GRID)
Better to use alternatives:
Files associated with a TIF raster file
e.g. DEM
From contours: topo to raster
ASCII to raster
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Assembling data lab (#2):
DEM import ASCII
- Creates integer values
DEM Topo to Raster (from contours)
- Creates decimal values
Many raster operations can’t be used on non-integer values
e.g. histograms
More raster formats
read by ArcGIS
.PIX (PCI Geomatica)
.IMG (ERDAS Image)
.GEOTIFF (no .tfw needed)
.JPG plus .wld or .jpgw
(georeferencing)
This jpg cat has no .wld/jpgw file
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Projections and ellipsoids
Data layers can be displayed ‘on the fly’
They must be the same projection for analysis
Two ways to change projection for a layer:
1. Use Project tool and know the projection parameters
2. Data -> export data (using data frame projection)
Note: ensure data layer projection / first layer loaded is
in the desired projection
BC: UTM zones
How do we deal with multiple UTM zones: Eastings coordinates switch from ~700,000 at
the east edge of one zone to ~300,000 at the west edge of the next (= same place)
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BC Albers projection
Central meridian: 126 W
First Standard Parallel: 50N
Second Standard Parallel: 58:30N
Latitude of projection origin 45N
False northing 0
False easting 1000000 (1million m)
Summary: BC mapping coordinates
BC geomatics industry ‘recognises’:
1. Geographic – latitude / longitude
– data storage
2. Universal Transverse Mercator (UTM): zones 7-11 - local / regional
3. BC Albers
- provincial data
View all 3 on imap BC: http://maps.gov.bc.ca/ess/sv/imapbc
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Modeling the Earth: ellipsoids and projections
ellipsoids for data also have to match
• Geoid - surface at mean sea level and is used for measuring
heights represented on maps’
• Ellipsoid (Spheroid) – Measure location (latitude and
longitude) of points of interest. Many different ellipsoids have been
defined for the world.
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