ArcGis Georeferencing a Map

8/11/2019 ArcGis Georeferencing a Map

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ArcGis Georeferencing a Map

ArcGIS is a geographic-information-system (GIS) developed byESRI.Being widely used andthe sheer amount of functions and add-ons are maybe the important causes for being a big-player at universities as well.

Therefore we will present you some basic tutorials for learning an enjoying ArcGIS:

Tutorial 1: how to georeference a scanned map in ArcGIS?

objective

To connect a scanned map with other geographical data the map needs to be refrenced. Thismeens, that every pixel in the scanned image gets a new dimension: besides its location in theimage (e.g. 326th pixel from left and 124th pixel from the top) it gets a real-world coordinate aswell (e.g. 4532 and 16N 1203711W ).The objective of this tutorial is to show you how to translate these pixel-coordinates in real-world coordinates, aka. Georeferenciation.

what do you need

ArcGIS 10, 9.3, 9.1, etc.a scanned map availbale as *.tif or *.jpg (other flavours can be used as well, but should beratser)(weve used a topographic map 1:25.000 (4521) distributed by the HessischesLandesvermessungsamt (1983)

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step 1: define a projection

In the first step we need to define a projectionfor the map: so the same term is also the function in

ArcGIS:Define Projection (Abb.1).

Fig.1 Location of Define Projection in the ArcGIS Toolbox


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In the toolDefine Projectionwe choose the scanned map asInput Dataset(Fig.2 red 1.) and the

coordiante system that is defined in the description of the map (Fig.2 red 2.).

Fig. 2 Input of parameters



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step 2: preparation of the georeferenciation

Now we need to adjust the visibility of the Georeferencing Toolbar. Look at Fig. 3 an follow the four

steps.

Fig.3 Add the Georeferencing Toolbar

First open theEditor(red 1.). There we choose Toolbar options ->Customize(red 2.) and a list with

available toolbarswill be opened (rot 3.). Now search for the Georeferencingand check it. The Toolbar

shows up in your working window (red 4.).



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step 3: georeferencing

Zoom to the upper left edge of the map and search for a crossing of a longitude and latitude. Now createa point on this cross using the functionAdd Control Points(Fig.4 red 1.). After marking the point use a

right-click (red 2.) and choose the optionInput X and Y: a window will open (red 3.) where you can

record your pairs of input and output coordinates. Record the values that belongs to the latitude andlongitude as Y- and X-value. Do this for the other three edges of the map as well! if you dont want to

struggle with auto-projection use always opposing pairs (lower left, upper right, upper left, lower right).

Fig.4 adding control-points



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As the transformation we will use 1st Order Polynomial(look here: Georeferencing->Transformation.

The result of the transformation needs to be exported (Fig.5) using a right-click on the layer:Data->Export Data. It is important to give a name, file format and the storage place for the resulting raster in

theExport Datadialogue.

Fig.5 export as TIFF

step 4quality control

As a minimal quality control you should compare the coordinates of the map and the shown coordinates

on the program. The new coordinates will eb shown on the lower right part of the working window. Ifthey match you have done everything right.

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ArcGis Georeferencing a Map