Most radio astronomical observations are affected to some degree by man-made and natural interference. There are a few avoidance techniques that can reduce the impact of interference on the survey, but we must make quite significant advances in the understanding of our antennas and receivers and the interference itself before a substantial improvement can be expected. A major increase in the efficiency of future surveys will likely come from phased-array feeds, which have the potential for much closer beam spacings, greater antenna efficiency, and wider fields of view than current independent-feed arrays.

Recent neutral hydrogen (HI) surveys have detected enough sources to make initial predictions of the extragalactic HI luminosity function. These surveys provide useful pointers for the Parkes Multibeam Survey, highlighting various advantages and disadvantages of different observing and analysis procedures. The newest surveys are also large enough to permit some statistical tests of their completeness. The detection rates clearly fall short of what would be expected based on a simple propagation of errors, suggesting the need for further development of detection software. I suggest several procedures for determining the effective sensitivity of HI surveys. Applied to two recent Arecibo surveys, these suggest that the HI luminosity function may be much steeper than its optical counterpart, and that the Parkes surveys may detect a large number of low-mass sources.

The vast quantities of data produced by modern radio telescopes require advanced visualisation tools to explore them. The quantitative nature of astronomy requires more than just representing data visually. This paper discusses research in displaying, and using, a three-dimensional ‘cursor’ in amorphous, noisy data which often resemble wispy tendrils.

The parameters of the HI Parkes All-Sky Surveys (HIPASS), as proposed by the Multibeam Survey Working Group, are described, as are the advantages and disadvantages of various multibeam observing techniques, including telescope scanning. The best techniques, in terms of minimising the variance in image sensitivity, are calculated. Some of the observing techniques may be applicable to other multibeam surveys.

The results of 21 cm HI survey observations are presented for two fields, centred on the Centaurus and Fornax southern galaxy clusters. One previously uncatalogued dwarf galaxy was detected near the southern edge of the Fornax cluster, and is visible on UKST survey plates. Implications for the Parkes Multibeam All Sky Survey are discussed.

HI structure is seen at every scale down to the angular resolution limit of all survey telescopes. I present several examples of the structures at high Galactic latitudes with the 12 arcmin beam of the Loveli Telescope, the 2 arcmin resolution of the DRAO synthesis, as well as other indicators of finer scale structure in the interstellar medium (ISM).

The parameters of a new Australia Telescope Compact Array (ATCA) mosaic of the Large Magellanic Cloud (LMC) in the 21-cm line of neutral hydrogen are described. A preliminary peak-brightness-temperature image of the whole of the LMC, and a detailed image of the region around the supergiant shells LMC 4 and 5 is shown.

I present new high-resolution observations of the HI in NGC 4214 made as part of a study of the small-scale kinematics and star formation regions of the galaxy.

We describe a major Anglo-Australian project to undertake a UKST Ha survey of the Southern Galactic plane, Magellanic clouds and selected regions. The survey will use a new 12 × 12 inch monolithic Hα interference filter of high specification and Tech Pan film which offers significant advantages over other emulsions due to its peak sensitivity at Ha and its extremely fine grain, high resolution, exceptional DQE, excellent imaging and low noise. A survey of unprecedented area coverage, depth and resolution should result, superior to any previous optical survey of ionised gas in the galaxy. It is certain to lead to exciting new discoveries and new avenues of research.

The DEep Near-Infrared Survey of the southern sky (DENIS) will produce an important by-product: a clean, complete view of the local Universe to z ∼ 0·07 for 105 galaxies. We identify the FLAIR multi-fibre system on the UKST as an extremely competitive facility to undertake follow-up spectroscopy for this sample due to the need to cover wide areas of sky and observe thousands of objects to a relatively bright (B < 17·5) magnitude.

A problem for studies of large scale structures in nearby space (cz < 10,000 km s-1) is the presence of the Zone of Avoidance which is so large and wide on the sky that potentially important clusters and voids remain undetected. A prime example was the Ophiuchus cluster discovered by Wakamatsu and Malkan (1981) as a heavily obscured cD cluster close to the Galactic centre region (l = 0·5°, b = +9·5°). It is the second brightest X-ray cluster after Perseus. A hidden galaxy survey was performed by visually searching ESO/SERC Sky Survey (R and J) copy films of the region centred at l = 355°, b = +10° finding more than 4000 galaxies in six fields. Several irregular clusters adjacent to Ophiuchus were found forming a supercluster which may be connected to the Hercules supercluster by a wall structure parallel to the local supergalactic plane (Wakamatsu et al. 1994). In front of this supercluster, an 'Ophiuchus Void' is suggested (cz = 4,500 km s-1). The Ophiuchus supercluster at cz = 8,500 km s-1 is similar to the Hercules supercluster (cz = 11,000 km s-1), and extends north toward the latter supercluster.

Results from the Arecibo HI Strip Survey, an unbiased extragalactic HI survey, combined with optical and 21 cm follow-up observations, determine the HI mass function and the cosmological mass density of HI at the present epoch. Both are consistent with earlier estimates, computed for the population of optically selected galaxies. This consistency occurs because, although the distribution of optical central surface brightnesses among galaxies is flat, we fail to find a population of galaxies with central surface brightnesses fainter than 24 B-mag arcsec−2, even though there is no observational selection against them.