Geospatial data considerations
Quality/Reliability
Temporal
Spatial
Themes or attributes
What categories are used?
Are categories relevant?
Are the data verified?
Which organisation/individual created them?
Cloud cover issues.
Availability of data from decades ago.
Frequency and timing of observations, if repeated surveys are needed
Spatial resolution (whether the data is 1x1 km), or 50x50 km.
Ownership of data - is it freely available?
What format is data stored in?
Old paper maps may be damaged, difficult to read
need for georeferencing and georectification
Resolution of data sources may depend on your locaion, e.g. Google doesn't have aerial photography for remote Indonesian islands!
Data needs might be seasonal or a short period of time, but satellites might not pass over at the right time
Project/Research Aims
What questions are you trying to answer?/
What are you trying to achieve?
What data do you need to answer those questions/achieve those aims/goals?