Just a few more words of explanation to Giovanni's answers...
On 09/28/2010 08:06 PM, Giovanni Manghi wrote:
Hi,
1. I tried doing this with Join Attributes and selecting the CSV file.
However I found that when QGIS reads in the CSV file, it casts all of
the columns as Text, so I couldn't use the numerical values. I notice
the Join Attributes from CSV feature is new in QGIS 1.5.0. Maybe there
is a bug?
you can do Joins with dbf tables. New join features are being developed.
In case you're using Excel 2007, you no longer have support for the
(important) dbf format. So get a copy of Openoffice.org and use that to
export your tables to dbf. Then number columns will stay as numbers for
the import to QGIS.
If there's any problem with the numbers being exported as text, then
rewrite the column headers in the Excel (OOo Calc) to explicitly make
them numbers in dbf format. For example a column header like:
Value,N,10
will force the dbf column to be numeric with 10 digits.
2. Eventually I will want to put my data into a database. I notice I
can choose between SpatiaLite and PostGIS. Which is easier to use? Is
there a performance difference?
among the others, Postgis is an extension of PostgreSQL, so is server
based, spatialite is file based.
In addition, Spatialite is easy. PostGIS will perform better on huge tables.
3. In ArcMap, I frequently used the capability to vary the thickness
of line features according to a value in the attribute table. I notice
that this capability is available in QGIS only for points ("drawing by
field") but not for line features. Is there another way to accomplish
variable thickness lines in QGIS? If not, is "drawing by field" for
line features under development?
new symbology -> advanced -> size scale field
I can't seem to get this to work (1.5 on Ubuntu 10.04).
What you can do is categorize the lines then manually give each a
different line width. In the Old Symbology, choose "Graduated symbol",
select the line width column and click Classify. Then change the width
of each line. Or, Using the "New Symbology" , choose "Classified", then
again select the column and click Classify. Then double click on each
symbol to change its width.
Regards,
Micha
cheers
-- Giovanni --
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--
Micha Silver
Arava Development Co. +972-52-3665918
http://surfaces.co.il
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