Mapping and modeling species distributions
Department of Botany and Zoology, Masaryk University
Bi9661 Selected issues in Ecology, Autumn 2013
Borja Jiménez-Alfaro, PhD
Part 1:
MAPPING
SCALE, EXTENT, GRAIN AND ACCURACY
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1)
Understand the format of observational data (Occurrences)
Import the occurrences into Diva-GIS and create a SHAPEFILE
First contact with GIS???
Objectives of this practice
2)
Understand the format of GIS environmental variables
Assess the fit between occurrences and GIS layers
3)
INSTALLATION OF DIVA-GIS and MAXENT
PREPARATION of INPUT FILES
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What is a GIS?
Geographic Information System
“A system for capturing, storing, checking, integrating,
manipulating, analysing and displaying data which are spatially
referenced to the Earth. This is normally considered to involve a
spatially referenced computer database and appropriate
applications software”
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What is a GIS?
Digital
Mapping
Photo-
grammetry
Computer
Aided
Design
Surveying
Remote
Sensing
Databases
GIS
Cross-disciplinary nature of GIS
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Two main types of data
Attribute data (the INFORMATION)
Says what a feature is
Eg. statistics, text, images, sound, etc.
Spatial data (the GEOGRAPHY)
Says where the feature is
Co-ordinate based
Vector data – discrete features (points, lines, polygons)
Raster data – A continuous surface
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Layers: RASTER vs. VECTORIAL
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Software – ArcGIS
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Software - IDRISI
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Software – GRASS GIS (Free)
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100% Free
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Software – DIVA-GIS (free)
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Basic concepts
Scale and extent
In spatial ecology, scale refers to the spatial extent of ecological
processes and the spatial interpretation:
LOCAL, REGIONAL, GLOBAL
In the GIS world, scale is the relationship of the distance on
the map/data to the actual distance on the ground, and
extent refers to the dimension of the layers
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Basic concepts
Resolution
= Grain
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Basic concepts
Accurary
the degree or closeness to which the information on a
map matches the real world
Precision
refers how exact is the description of data
Important issues for spatial analyses
e.g. to test the fit between your occurrences and the variables
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Accuracy < 1 m
(Submetric GPS)
Accuracy 5 m (GPS)
Accuracy 10 m (GPS)
Imagine one location and its coordinates at precision = 1 m
(e.g. X235698, Y4785632)
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5 m
Topographic gradient: accuracy matters¡
At this scale, you need
precision and accuracy
of < 5 m
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Accuracy 1 km
Accuracy 5 km
Accuracy 10 km
Imagine one location and its coordinates at precision = 1 km
(e.g. X235, Y4785)
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5 km
Landscape units: accuracy matters¡
At this scale, you need
precision and accuracy
of < 5 km
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Coordinate System
The main format is Latitude and Longitude,
Generally in decimal degrees
However it produces cells of different sizes
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Coordinate systems
Different projections are used to represent a given region
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Coordinate systems
The projection is corrected with the DATUM
to represent the real surface of the Earth
In Europe: datum ETRS89 is the new standard
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IMPLICATIONS
1. Verify the reference system for your coordinates
2. Verify the datum used for that reference system
3. Try to understand the accuracy of that coordinates
4. You can transform coordinates and datums in GIS
5. The same procedure fotr VECTORIAL and RASTER layers
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Our data
We will use geographical coordinates (log/lat) in decimal degrees
In DIVA-GIS manual it is indicated how to transform from DDGGSS
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The PRACTICE
Prepare the coordinates in EXCEL
Create a SHAPEFILE of occurrences in Diva-GIS
Import the raster variables from ASCII file to DIVA-GIS
Save the layers and the project in your computer
Check the extent and grain of rasters and the accuracy of data
ADVANCED STUDENTS:
Revision of projections and datum, spatial autocorrelation in ArcGIS